Beam steering element and associated methods for manifold fiberoptic switches and monitoring

ABSTRACT

An optical system comprising a combination optical switch and monitoring system based on an array of mirrors, and a moveable reflective element co-packaged together, including discrete sets of fiber ports wherein λn from input fiber ports is focused on λn mirror via the use of shared free space optics; such as shared beam steering elements, dispersive elements, and optical elements, and discrete arrays of MEMS mirrors utilized to select and switch selected wavelengths from the input fiber port(s) to an output fiber port(s) of the optical switch, and wherein a moveable reflective element sharing the same free space optics is utilized to sweep across and reflect selected portions of the optical spectrum back to a photodetector. By correlating reflective element position with power measured, a processor can obtain a spectral plot of the wavelength band of interest, as well as calculate parameters such as center wavelength, passband shape, and OSNR.

CROSS-REFERENCE AND PRIORITY CLAIM TO RELATED APPLICATION

To the full extent permitted by law, the present United StatesNon-Provisional patent application, is a Continuation-in-Part of, andhereby claims priority to and the full benefit of, United StatesNon-Provisional patent application entitled “SEGMENTED PRISM ELEMENT &ASSOCIATED METHODS FOR MANIFOLD FIBEROPTIC SWITCHES,” filed on Jun. 12,2007, now U.S. Pat. No. 7,720,329 having assigned Ser. No. 11/811,928,and hereby claims priority to and the benefit of United StatesProvisional patent application entitled “SEGMENTED PRISM ELEMENT ANDASSOCIATED METHODS FOR MANIFOLD FIBEROPTIC SWITCHES,” filed on Nov. 7,2006, having assigned Ser. No. 60/857,441; United States Non-Provisionalpatent application entitled “BEAM STEERING ELEMENT AND ASSOCIATEDMETHODS FOR MANIFOLD FIBEROPTIC SWITCHES,” filed on Oct. 18, 2007,having assigned Ser. No. 11/975,242; United States Non-Provisionalpatent application entitled “BEAM STEERING ELEMENT AND ASSOCIATEDMETHODS FOR MANIFOLD FIBEROPTIC SWITCHES AND MONITORING,” filed on Oct.25, 2007, having assigned Ser. No. 11/977,690; United StatesNon-Provisional patent application entitled “BEAM STEERING ELEMENT ANDASSOCIATED METHODS FOR MIXED MANIFOLD FIBEROPTIC SWITCHES,” filed onOct. 30, 2007, having assigned Ser. No. 11/980,974; and PatentCooperation Treaty patent application entitled “BEAM STEERING ELEMENTAND ASSOCIATED METHODS FOR MANIFOLD FIBEROPTIC SWITCHES AND MONITORING,”filed Oct. 31, 2007 having assigned Serial No. PCT/US07/22955; UnitedStates Non-Provisional patent application entitled “WAVELENGTH SELECTIVESWITCH HAVING DISTINCT PLANES OF OPERATIONS,” filed on Jul. 23, 2008,having assigned Ser. No. 12/220,356; United States Non-Provisionalpatent application entitled “WAVELENGTH SELECTIVE SWITCH WITH REDUCEDCHROMATIC DISPERSION AND POLARIZATION-DEPENDENT LOSS,” filed on Nov. 4,2008, having assigned Ser. No. 12/264,716; United States Non-Provisionalpatent application entitled “SYSTEM AND METHOD FOR ASYMMETRICAL FIBERSPACING FOR WAVELENGTH SELECTIVE SWITCHES,” filed on Aug. 19, 2008,having assigned Ser. No. 12/194,397; United States Non-Provisionalpatent application entitled “HIGH PORT COUNT INSTANTIATED WAVELENGTHSELECTIVE SWITCH,” filed on Mar. 29, 2009, having assigned Ser. No.12/413,568, filed on behalf of inventors, Michael L. Nagy and HarryWayne Presley, incorporated entirely herein by reference filed on behalfof inventors Harry Wayne Presley and Michael L. Nagy.

TECHNICAL FIELD

The present invention relates generally to all-optical fiber opticcommunications and datacom switches, and more specifically pertains tofiber optic switches used in multi-wavelength networks.

BACKGROUND

Modern communications networks are increasingly based on silica opticalfiber which offers very wide bandwidth within several spectralwavelength bands. At the transmitter end of a typical point-to-pointfiber optic communications link an electrical data signal is used tomodulate the output of a semiconductor laser emitting, for example, inthe 1525-1565 nanometer transmission band (the so-called C-band), andthe resulting modulated optical signal is coupled into one end of thesilica optical fiber. On sufficiently long links the optical signal maybe directly amplified along the route by one or more amplifiers, forexample, optically-pumped erbium-doped fiber amplifiers (EDFAs). At thereceiving end of the fiber link, a photodetector receives the modulatedlight and converts it back to its original electrical form. For verylong links the optical signal risks becoming excessively distorted dueto fiber-related impairments such as chromatic and polarizationdispersion and by noise limitations of the amplifiers, and may bereconstituted by detecting and re-launching the signal back into thefiber. This process is typically referred to asoptical-electrical-optical (OEO) regeneration.

In recent developments, the transmission capacity of fiber optic systemshas been greatly increased by wavelength division multiplexing (WDM) inwhich multiple independent optical signals, differing uniquely bywavelength, are simultaneously transmitted over the fiber optic link.For example, the C-band transmission window has a bandwidth of about 35nanometers, determined partly by the spectral amplification bandwidth ofan EDFA amplifier, in which multiple wavelengths may be simultaneouslytransmitted. All else being equal, for a WDM network containing a numberN wavelengths, the data transmission capacity of the link is increasedby a factor of N. Depending on the specifics of a WDM network, thewavelength multiplexing into a common fiber is typically accomplishedwith devices employing a dispersive element, an arrayed waveguidegrating, or a series of thin-film filters. At the receiver of a WDMsystem, the multiple wavelengths can be spatially separated using thesame types of devices that performed the multiplexing and thenseparately detected and output in their original electrical datastreams.

Dense WDM (DWDM) systems are being designed in which the transmissionspectrum includes 40, 80, or more wavelengths with wavelength spacing ofless than 1 nanometer. Current designs have wavelength spacing ofbetween 0.4 and 0.8 nanometer, or equivalently a frequency spacing of 50to 100 GHz respectively. Spectral packing schemes allow for higher orlower spacing, dictated by economics, bandwidth, and other factors.Other amplifier types, for example Raman, that help to expand theavailable WDM spectrum are currently being commercialized. However, thesame issues about signal degradation and OEO regeneration exist for WDMas with non-WDM fiber links. The expense of OEO regeneration iscompounded by the large number of wavelengths present in WDM systems.

Modern fiber optic networks are evolving to be much more complicatedthan the simple point-to-point “long haul” systems described above.Instead, as fiber optic networks move into the regional, metro, andlocal arenas, they increasingly include multiple nodes along the fiberspan, and connections between fiber spans (e.g., mesh networks andinterconnected ring networks) at which signals received on one incominglink can be selectively switched between a variety of outgoing links, ortaken off the network completely for local consumption. For electroniclinks, or optical signals that have been detected and converted to theiroriginal electrical form, conventional electronic switches directlyroute the signals to their intended destination, which may then includeconverting the signals to the optical domain for fiber optictransmission. However, the desire to switch fiber optic signals whilestill in their optical format, thereby avoiding expensive OEOregeneration to the largest extent possible, presents a new challenge tothe switching problem. Purely optical switching is generally referred toas all-optical or OOO switching optical/optical (OOO).

Switching

In the most straightforward and traditional fiber switching approach,each network node that interconnects multiple fiber links includes amultitude of optical receivers which convert the signals from optical toelectrical form, a conventional electronic switch which switches theelectrical data signals, and an optical transmitter which converts theswitched signals from electrical back to optical form. In a WDM system,this optical/electrical/optical (OEO) conversion must be performed byseparate receivers and transmitters for each of the W wavelengthcomponents on each fiber. This replication of expensive OEO componentsis currently slowing the implementation of highly interconnected meshWDM systems employing a large number of wavelengths.

Another approach for fiber optic switching implements sophisticatedwavelength switching in an all-optical network. In a version of thisapproach that may be used with the present Wavelength Selective Switch(WSS) configuration, the wavelength components W from an incomingmulti-wavelength fiber are demultiplexed into different spatial paths.Individual and dedicated switching elements then route thewavelength-separated signals toward the desired output fiber port beforea multiplexer aggregates the optical signals of differing wavelengthsonto a single outgoing fiber. In conventional fiber switching systems,all the fiber optic switching elements and associated multiplexers anddemultiplexers are incorporated into a wavelength selective switch(WSS), which is a special case of an enhanced optical cross connect(OXC) having a dispersive element and wavelength-selective capability.Additionally, such systems may incorporate lenses and mirrors whichfocus light and lenslets which collimate such light.

Advantageously, all the fiber optic switching elements can beimplemented in a single chip of a micro electromechanical system (MEMS).The MEMS chip generally includes a two-dimensional array of tiltablemirrors which may be separately controlled. U.S. Pat. No. 6,097,859 toSolgaard et al., incorporated herein in its entirety, describes thefunctional configuration of such a MEMS wavelength selective switch(WSS), which incorporates a wavelength from an incoming fiber and iscapable of switching wavelength(s) to any one of multiple outgoingfibers. The entire switching array of several hundred microelectromechanical system (MEMS) mirrors can be fabricated on a chiphaving dimension of less than one centimeter by techniques welldeveloped in the semiconductor integrated circuit industry.

Solgaard et al. further describes a large multi-port (including multipleinput M and multiple output N ports) and multi-wavelength WDM wavelengthselective switch (WSS), accomplishing this by splitting the WDM channelsinto their wavelength components W and switching those wavelengthcomponents W. The Solgaard et al. WSS has the capability of switchingany wavelength channel on any input port M to the output fiber port N,wherein N=1. Moreover, each MEMS mirror in today's WDM wavelengthselective switch is dedicated to a single wavelength channel whether ittilts about one or more axes.

EDFAs or other optical amplifiers may be used to amplify optical signalsto compensate loss, but they amplify the entire WDM signal and theirgain spectrum is typically not flat. Therefore, measures are needed tomaintain the power levels of different signals at common levels or atleast in predetermined ratios.

Monitoring

Monitoring of the WDM channels is especially important in opticaltelecommunication networks that include erbium doped fiber amplifiers(EDFAs), because a power amplitude change in one channel may degrade theperformance of other channels in the network due to gain saturationeffects in the EDFA. Network standard documents, such as the BellcoreGR-2918, have been published to specify wavelength locations, spacingand signal quality for WDM channels within the networks. Networkperformance relative to these standards can be verified by monitoringwavelength, power and signal-to-noise ratio (SNR) of the WDM channels.

A multi-wavelength detector array or spectrometer may be integrated intothe free space of a WSS and utilized to monitor wavelength channels,power and signal-to-noise ratio (SNR) in telecommunication networks.Typically, a portion of the WDM channels are diverted by a splitter orpartially reflective mirror to an optical power monitor or spectrometerto enable monitoring of the WDM channels. Each MEMS mirror in today'sWDM wavelength selective switch (WSS) is dedicated to a singlewavelength channel. Whether it tilts about one or more axes, such mirrormay be used to control the amount of optical power passing through WSSfor such single wavelength channel. In addition, a detector array orspectrometer may be external to the free space of the WSS or OXC, andmay be utilized to monitor white light (combined wavelength channels)power, and signal-to-noise ratio of optical signal via input/outputfiber port taps or splitters. More specifically, the prior art consistsof costly large two-dimensional detector arrays or spectrometer utilizedto monitor multiple input or output wavelength channels, power andsignal-to-noise ratio.

Monitoring and switching are part of a feedback loop required to achieveper-wavelength insertion loss control and such systems comprise threeclassic elements: sensor for monitoring, actuator for multi wavelengthswitching and attenuating, and processor for controlling wavelengthswitching, selection and equalization. The actuator in today's WSSproducts is typically a MEMS-based micromirror or a liquid crystalblocker or reflector. The sensor is typically a modular optical powermonitor, comprising a mechanical filter for wavelength selection and aphotodetector. Depending on the system, the three elements can beco-located in the same device, or can exist as separate standalone cardsconnected by a backplane.

In general, higher levels of integration of the sensor, actuator, andprocessor are attractive from a size, cost, speed, and simplicity ofoperation standpoint. The proposed new solution reaps these benefitsbecause of a very high level of integration.

Nonetheless, it is readily apparent that there is a recognizable unmetneed for an improved WDM wavelength selective switch that allows forinexpensive monitoring of a full spectrum of the output optical signaland wherein the switching node demultiplexes the aggregatemulti-wavelength WDM signal from input fibers into its wavelengthcomponents, spatially switching one of many single-wavelength componentsfrom different input fibers for each wavelength channel, and whereinsuch switch multiplexes the switched wavelength components to one outputfiber for retransmission; and wherein such wavelength components' powermay be monitored and varied by controllable attenuation, resulting in ahigher level of integration of the sensor, actuator, and processor; andwherein such power monitoring comprises continuous monitoring over theentire spectrum of interest, including wavelengths that lie between thesignal wavelengths, enabling calculation of key parameters such ascenter wavelength, passband shape, and Optical Signal to Noise Ratio(OSNR) for the optical signals of interest; thereby enabling a switchand monitoring system based on a moveable reflective element in a singledevice capable of utilizing common optical components.

BRIEF SUMMARY

Briefly described in a preferred embodiment, the present inventionovercomes the above-mentioned disadvantages and meets the recognizedneed for such an optical switch by providing an optical systemcomprising a combination optical switch and monitoring system based on amoveable reflective element co-packaged together comprising discretesets of fiber ports, the optical switch configured either with N inputfiber ports and 1 output fiber port (N×1 optical switch) or with 1 inputfiber port and N output fiber ports (1×N optical switch), and wherein λnfrom said input fiber ports is focused on λn mirror via the use ofshared free space optics; such as one or more shared beam steeringelements, one or more dispersive elements, and one or more opticalelements, wherein said one or more steering elements steers one or moreλn from any point in the optical path to any other point; and one ormore discrete arrays of micro electromechanical system (MEMS) mirrors ina shared array, wherein said array of MEMS mirrors is utilized to selectand switch selected wavelengths from the input fiber port(s) to anoutput fiber port(s) of the optical switch, and wherein a moveablereflective element using and sharing the same free space optics as theMEMS array is utilized to select and reflect selected portions of thewavelength spectrum between input and output monitoring fiber portsbelonging to the monitoring system; wherein the moveable reflectiveelement may be utilized to select individual wavelengths or spectralcomponents from its input monitoring fiber ports to send to its outputmonitoring fiber port for optical power or other internal feedbackmonitoring and dynamic insertion loss control of a switching node intelecommunication networks.

According to its major aspects and broadly stated, the present opticalsystem in its preferred form is a discrete fiber optic switch enabled bythe beam steering element (BSE), comprising input fiber ports, freespace optics (FSO) (including but not limited to various lenses, adispersive element for spatially separating/combining the wavelengthcomponents of the aggregate multi-wavelength WDM signal, and the BSE),an array of MEMS mirrors whose individual mirrors correspond to uniquewavelengths operating within the WDM network (for example, mirror #1corresponding to λ#1 and receiving λ#1 from all input fiber ports,wherein by moving moveable MEMS mirror #1, the preferred optical path isgenerated via beam steering between an input fiber port and the outputfiber port of the N×1 configuration, this being repeated independentlyfor every wavelength in each optical switch of the optical system andfor every MEMS mirror), wherein such switch multiplexes the MEMS-steeredwavelength components from various input fiber ports to one output fiberport for re-transmission, and wherein the moveable reflective elementmay be utilized to select individual wavelengths or spectral componentsfrom its input monitoring fiber ports to send to its output monitoringfiber port for optical power or other monitoring while simultaneouslysharing the other free space optic (FSO) components described above.Analogously, the light direction may be arbitrarily reversed from theabove description so that wavelengths may be switched from a singleinput fiber port to any of a number of output fiber ports (1×N) withoutrestriction on which wavelength is routed to which output port.

A co-packaged optical switch and optical spectrometer for switching andmonitoring one or more optical signals, the signals comprising one ormore optical wavelengths, each optical wavelength constituting a workpiece, the optical switch and optical spectrometer further comprising:

one or more input fiber ports, each input fiber port serving as anexternal interface for introducing one or more input optical signalsinto the optical switch;

one output fiber port, the output fiber port serving as an externalinterface for extracting the output optical signal from the opticalswitch;

one or more shared optical elements, wherein each optical elementfocuses the one or more optical signals of the one or more input fiberports and the optical signal of the one output fiber port;

at least one shared wavelength dispersive element for spatiallyseparating at least one first wavelength of one of the one or more inputoptical signals from at least one other wavelength of the input opticalsignal and for recombining at least one first wavelength of a selectedinput optical signal of the one or more input optical signals with atleast one other wavelength of the one or more input optical signals toform the output optical signal;

an array of switching elements, at least one switching element forreceiving one wavelength from each of the one or more input fiber portsand for switching one selected wavelength from one of the one or moreinput fiber ports to the one output fiber port according to a positionof the at least one switching element;

a tap for coupling a portion of the one output fiber port optical signalto at least one input monitoring port;

at least one moveable reflective element for translating laterallyacross a selected band of the optical spectrum of the portion of the oneoutput fiber port optical signal as projected by the wavelengthdispersive element, and for reflecting a narrow band of the selectedband of the optical spectrum to an output monitoring fiber portaccording to a position of the moveable reflective element;

at least one beam steering element configured to position eachwavelength from each of the one or more input fiber ports onto adesignated switching element of the array of switching elements, toposition at least one selected wavelength from the switching element tothe output fiber port, and to position the optical spectrum of theportion of the one output fiber port optical signal projected by thewavelength dispersive element onto the at least one moveable reflectiveelement; and,

an optical measurement device for receiving the narrow band of theselected band of the optical spectrum from the output monitoring fiberport and for measuring an optical power of the narrow band of theselected band of the optical spectrum.

A co-packaged optical switch and optical spectrometer for switching andmonitoring one or more optical signals, the signals comprising one ormore optical wavelengths, each optical wavelength constituting a workpiece, the optical switch and optical spectrometer further comprising:

one input fiber port, the input fiber port serving as an externalinterface for introducing the input optical signal into the opticalswitch;

one or more output fiber ports, each output fiber port serving as anexternal interface for extracting one or more output optical signalsfrom the optical switch;

one or more shared optical elements, wherein each the optical elementfocuses the optical signal of the one input fiber port and the one ormore optical signals of the one or more output fiber ports;

at least one shared wavelength dispersive element for spatiallyseparating at least one first wavelength of the input optical signalfrom at least one other wavelength of the input optical signal and forrecombining at least one first wavelength of the output optical signalwith at least one other wavelength of the output optical signal;

an array of switching elements, at least one switching element forreceiving at least one wavelength from the one input fiber port andswitching at least one wavelength of the one input fiber port to one ofthe one or more output fiber ports according to a state of at least oneshared arrayed switching element;

at least one tap on at least one of the one or more output fiber portsfor coupling a portion of the at least one of the one or more outputfiber ports optical signal;

an optical combiner for receiving one or more the portion of the atleast one of the one or more output fiber ports optical signal and forcombining the one or more the portion of the at least one of the one ormore output fiber ports optical signal, wherein the optical combinercouples the one or more the portion of the at least one of the one ormore output fiber ports optical signal into an input monitoring port;

at least one moveable reflective element for translating laterallyacross a selected band of the optical spectrum of the one or more theportion of the at least one of the one or more output fiber portsoptical signal as projected by the wavelength dispersive element, andfor reflecting a narrow band of the selected band of the opticalspectrum to an output monitoring fiber port according to a position ofthe moveable reflective element;

at least one shared arrayed steering element for steering the at leastone wavelength from the one input fiber port onto the at least oneswitching element, and for steering the at least one wavelength from theat least one switching element to any of the one or more output fiberports and to position the optical spectrum of the one or more of theportion of the at least one of the one or more output fiber portsoptical signal projected by the wavelength dispersive element onto theat least one moveable reflective element; and

an optical measurement device for receiving the one or more of theportion of the at least one of the one or more output fiber portsoptical signal and for measuring an optical power of the narrow band ofthe selected band of the optical spectrum.

A device in a co-packaged optical switch and optical spectrometer, thedevice configured to reflect a selected portion of a wavelength spectrumof an optical signal, the device comprising:

a moveable element for receiving the wavelength spectrum and forreflecting a selected portion of the wavelength spectrum according to aposition of the moveable element, the moveable element comprising areflective area positioned on the moveable element for performing thereflecting; and

one or more shared optical elements, wherein each optical elementfocuses, disperses, multiplexes, steers, or otherwise conditions thewavelength spectrum.

A method of measuring a selected portion of a wavelength spectrumcomprising:

focusing the wavelength spectrum utilizing one or more shared opticalelements;

switching the wavelength spectrum from at least one input fiber port toat least one output fiber port;

receiving a selected portion of the wavelength spectrum; and

positioning a moveable reflective element to reflect a selected band ofthe selected portion of the wavelength spectrum back through the sharedoptical elements to an optical power measurement device.

Accordingly, a feature of the present optical system is its ability tofocus wavelength components of a set from any or all of the input fiberports onto a single MEMS mirror, enabling such mirror to select theinput port wavelength component to be switched to the output fiber portin an N×1 switch, and to do so for manifold switches operatingindependently and in parallel while sharing all FSO components withinthe same physical housing.

Another feature of the present optical system is its ability to measurethe full spectral profile of the optical signals found on the outputmonitoring fiber port, enabling the processor to calculate per-channelpower, center wavelength, passband shape, optical signal-to-noise ratio(OSNR), and passband ripple.

Another feature of the present optical system is its ability to providean optical system comprising Re-write independent claims

Still another feature of the present optical system is its ability toprovide one or more taps or splitters for coupling power from inputand/or output fiber ports.

Yet another feature of the present optical system is its ability toprovide full spectrum monitoring of input fiber ports utilized toreceive tapped or other multi-wavelength WDM signals for the purpose ofoptical power or other quality-of-signal measurements.

Yet another feature of the present optical system is its ability toreuse (share) the same free space optics (various lenses, mirrors, frontend optics, and back end optics for focusing wavelength components ofthe aggregate multi-wavelength WDM signal, dispersive element forspatially separating/combining the wavelength components of theaggregate multi-wavelength WDM signal), housing, mounts, and controlelectronics for all co-packaged switches and spectral monitor.

Yet another feature of the present optical system is its ability toprovide an optical path (i.e., an optical bridge) between two or moreswitches to create a form of M×N switch.

Yet another feature of the present optical system is its ability toprovide for ganged switching functionality of the manifold switch,wherein the MEMS mirrors, corresponding to a certain WDM wavelength, aremoved, rotated or tilted synchronously between all arrays of MEMSmirrors in the manifold switch, wherein the same switch state is createdfor all switches in the manifold switch on a per wavelength basis.

Yet another feature of the present optical system is flexibility whereinan almost limitless range of configurations may be obtained, whereinconfiguration variations may include number of input and output fiberports, number of switches in the manifold, ganged switching operations,bridging between switches in the manifold, number and spacing ofwavelengths in the WDM system, number and origin of tapped and externalmonitoring ports, and the like.

Yet another feature of the present optical system is its ability to becalibrated such that systemic effects are canceled and the switchingperformance improved, wherein systemic effects to be canceled mayinclude, for example, imperfect MEMS mirrors, assembly and componentimperfections, minor misalignments of components, environmental effects,and the like, and wherein the obtained calibration data is stored in anelectronic memory that can be accessed in real-time in support ofswitching control and command.

Yet another feature of the present optical system is its ability toutilize a single MEMS array of mirrors for selecting at least onewavelength component from any of the fibers for each wavelength of themulti-wavelength WDM signal, and wherein such array directs the selectedwavelength component to the output fiber of the N×1 optical switch inthe same physical housing.

Yet another feature of the present optical system is its ability toprovide a combination of fixed and adjustable mounts for shared freespace optics and dispersive element, fiber channel array (FCA), beamsteering element (BSE), continuous optical monitoring element, and a rowof MEMS mirrors for positioning and adjusting shared optical components.

Yet another feature of the present optical system, implemented as aco-packaged main switch and monitor switch, is its ability to utilize acontinuous optical monitoring element employing a linearly translatedmirror, for selecting any portion of the spectrum of WDM signals fromany of the tapped ports, and wherein such linearly translated reflectiveelement directs the selected spectral portion to one monitoring outputfiber port for optical power monitoring.

Yet another feature of the present manifold optical system is itsability to utilize a multi-mode fiber as the monitoring output fiber,leading to the photodetector, wherein the larger core of a multimodefiber increases the confidence that the true power of the intendedmeasurement is being captured with sufficient margin for MEMS mirrorpointing errors, environmental and aging effects, and the like, whereinthe coupling of light from free space into a fiber is vastly lesssensitive to positional errors for a multi-mode fiber than for thesingle-mode fibers typically used for telecom/datacom networks.

Yet another feature of the optical system is its ability to provide oneor more fiber ports carrying aggregate multi-wavelength WDM signals forthe purpose of monitoring the WDM signals, wherein the origin of the WDMsignals is arbitrary.

Yet another feature and advantage of the present optical system is itsability to self-monitor the aggregate multi-wavelength WDM signalspectrum at the input and/or output fiber ports of a manifold switch.

Yet another feature of the present optical system is its ability tomonitor signals within fibers, wherein signals to be monitored may beproduced by wideband optical power taps placed on the fibers to bemonitored, wherein other approaches make only approximate measurementsof signals by sampling them in free-space and therefore neglectingfree-space-to-fiber coupling effects.

Yet another feature of the present optical system is its ability, withregard to signal monitoring, to be calibrated such that systematiceffects are canceled and the measurement accuracy increased, whereinsystematic effects to be canceled may include the path-dependentinsertion loss of various optical paths through the system, imperfectlinearly translating reflective element, tap characteristics, assemblyand component imperfections, environmental effects, and the like,wherein so obtained calibration data are stored in an electronic memorythat can be accessed in real-time in order to provide corrections tosignal measurements in real-time.

Yet another feature of the present optical system is its ability toutilize the measurement of power levels of WDM wavelengths obtained viathe co-packaged monitoring functionality as a form of feedback to the1×N or N×1 switch, wherein the insertion loss of each wavelength throughthe switch may be actively adjusted to correct for mirror movementerrors, environmental effects, and the like, or similarly to producedesired spectral distributions of the aggregate multi-wavelength WDMsignals (for example, making the power levels of all wavelengths equalvia the selective attenuation of every wavelength), wherein theinsertion loss of each wavelength is controlled by the movement,rotation or tilting of the associated MEMS mirrors in the 1×N or N×1mirror array, wherein movement, rotation or tilting the MEMS mirror awayfrom its optimal angle of lowest insertion loss steers the free spacebeam arriving at the output port(s) and therefore misaligns the beamwith respect to the output fiber port(s) and introduces progressivelylarger insertion loss as the MEMS mirror is further tilted.

Yet another feature of the present optical system is its compatibilitywith using MEMS mirrors that can move, rotate or tilt around twoindependent axes of rotation, wherein the primary tilt axis is requiredfor fiber-to-fiber switching and the secondary tilt axis may be used forauxiliary purposes, wherein such auxiliary uses of the secondary tiltaxis may include insertion loss control, correction of component andassembly imperfections, environmental and aging effects, and the like.

Yet another feature and advantage of the present optical system is itsability to provide a means of power equalization, or other arbitraryspectral power distribution, of wavelengths wherein many beams fromdiverse sources are interchanged among network fibers.

Yet another feature of the present optical system is its ability toprovide uniformity of power levels across the WDM spectrum, or otherarbitrary spectral distribution, so that dynamic range considerations atreceivers and amplifier, non-linear effects, and crosstalk impairmentscan be minimized.

Yet another feature of the present optical system is its ability toprovide dynamic feedback control since the various wavelengths vary inintensity with time and relative to changes in optical channel routinghistory among the components.

Yet another feature of the present optical system is its ability toprovide a fiber optic switch with a means of power equalization ofwavelengths, and thus provide an aggregate multi-wavelength WDM signalenabling compensation for internal variations of opticalcharacteristics, misalignments, both integral to the device and as aresult of both manufacturing and environmental variation,non-uniformity, aging, and of mechanical stress encountered in theswitch.

Yet another feature of the present optical system is its ability toprovide wavelength switching and spectral monitoring in an opticalnetwork while reducing the cost and complexity of such optical network.

Yet another feature of the present optical system is its applicabilityfor non-WDM, or “white light” switching devices by the simple removal ofthe dispersive element and the subsequent simplification of the MEMSarray to a single MEMS mirror for each optical fiber in the manifoldsystem.

These and other features of the present optical switch will become moreapparent to one skilled in the art from the following DetailedDescription of the Preferred and Selected Alternate Embodiments andClaims when read in light of the accompanying Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present version of the invention will be better understood byreading the Detailed Description of the Preferred and AlternateEmbodiments with reference to the accompanying drawing figures, in whichlike reference numerals denote similar structure and refer to likeelements throughout, and in which:

FIG. 1 is a schematic illustration of a six input port by one outputfiber port wavelength selective switch (WSS) switch according to anembodiment of the present invention;

FIG. 2 is a schematic illustration of six input port by one output fiberport, dual channel MEMS mirror, output port taps, monitoring input fiberports, monitoring output fiber port, and monitor wavelengthcross-connect switch according to a preferred embodiment of the presentinvention;

FIG. 3A is a schematic illustration of an optical beam steering elementincluded in the WSS of FIG. 1;

FIG. 3B is a schematic illustration of an optical beam steering elementand facet angle equations entitled “Light Deflection Principle andEquations”;

FIG. 4 is a plan view of a single axis moveable mirror useable with thepresent invention;

FIG. 5A is a functional block diagram of a one input port by five outputfiber port wavelength selective switch with spectral monitor andfeedback control according to an alternate embodiment of the presentinvention;

FIG. 5B is a functional block diagram of a five input port by one outputfiber port wavelength selective switch with power monitor and feedbackcontrol according to a preferred embodiment of the present invention;

FIGS. 6A and 6B are cross sectional views illustrating two kinds ofmismatch in optically coupling a wavelength component beam to thewaveguide substrate according to an alternate embodiment of the presentinvention;

FIG. 7A is a top view of one instance of a fiber holder according to apreferred embodiment of the present invention;

FIG. 7B is schematically illustrated optical concentrator array usingplanar waveguide included in the N×1 WSS of FIGS. 1, 2 and 5B accordingto an alternate embodiment of the present invention;

FIG. 7C is schematically illustrated one instance of an opticalconcentrator array using planar waveguide included in the 1×N WSS ofFIG. 5A according to an alternate embodiment of the present invention;

FIG. 8 is a schematic view of the shared front end optics included inthe WSS of FIGS. 1 and 2;

FIG. 9A is a front face view of an illustrative MEMS mirror and fiveincident beams from the five input fiber ports according to anillustrative embodiment of the present invention;

FIG. 9B is a front face view of a second channel MEMS mirror and twoincident beams from the two monitoring input fiber ports according to anillustrative embodiment of the present invention;

FIG. 9C is a front face view of a third channel MEMS mirror and fiveincident beams from the five input fiber ports according to a preferredembodiment of the present invention as shown in FIG. 12;

FIG. 10 is a schematic illustration of a six input port by one outputfiber port prior art wavelength cross-connect switch;

FIG. 11 is an illustration of one instance of a typical single-row MEMSmirror array according to an embodiment of the present invention;

FIG. 12 is a three-dimensional schematic of a MEMS mirror according toan embodiment of the present invention of FIG. 9C;

FIG. 13 is a schematic illustration of a six input port by one outputfiber port wavelength selective switch according to preferred embodimentof the present invention;

FIG. 14 is a three-dimensional schematic of a wavelength selectiveswitch according to an alternate embodiment of the present invention;

FIG. 15 is a schematic illustration of a wavelength cross-connect withBSE-based architecture for creating manifold switches within the samepackage according to an embodiment of the present invention;

FIG. 16 is a schematic illustration of a wavelength selective switchwith BSE-based architecture FCLA-based optics of FIG. 10 according to analternate embodiment of the present invention;

FIGS. 17A and 17B are schematic illustrations of a 4-input-fiber by4-output-fiber optical switch, made up of four 1×N and four N×1wavelength selectable switches;

FIG. 18A is a schematic illustration of a five input port by one outputfiber port wavelength cross-connect switch according to an alternateembodiment of the present invention;

FIG. 18B is a schematic illustration of on instance of an optical beamsteering element included in the WSS of FIG. 18A;

FIG. 19A is a schematic illustration of a six input port by one outputfiber port wavelength selective switch according to an alternateembodiment of the present invention;

FIG. 19B is a schematic illustration of one instance of an optical beamsteering element included in the WSS of FIGS. 1 and 2, 19A;

FIG. 20 is a schematic illustration of a one input port by six outputfiber port wavelength selective switch according to an alternateembodiment of the present invention;

FIG. 21 is a schematic illustration of an input port by six output fiberport wavelength selective switch according to an alternate embodiment ofthe present invention;

FIG. 22A is a schematic illustration of a six input port by six outputfiber port wavelength selective switch according to an alternateembodiment of the present invention;

FIG. 22B is a schematic illustration of a six input port by six outputfiber port wavelength selective switch according to an alternateembodiment of the present invention;

FIG. 23 is a schematic illustration of a six input port by six outputfiber port wavelength selective switch according to an alternateembodiment of the present invention;

FIG. 24A is a top view diagram of an example embodiment of a linearlytranslating reflective element with a sliding reflective element;

FIG. 24B is a cross-sectional view diagram of an example embodiment ofthe linearly translating reflective element of FIG. 24A;

FIG. 24C is a top view diagram of an example embodiment of the sliderelement of the linearly translating reflective element of FIG. 24A;

FIG. 24D is a bottom view diagram of an example embodiment of the sliderelement of the linearly translating reflective element of FIG. 24A;

FIG. 24E is a top and cross-sectional view diagram of an exampleembodiment of the grooves in the substrate of the linearly translatingreflective element of FIG. 24A;

FIG. 24F is a top and cross-sectional view diagram of an exampleembodiment of the substrate of the linearly translating reflectiveelement of FIG. 24A with electrodes;

FIG. 25A is a cross-sectional view diagram of an example embodiment ofthe slider element of the linearly translating reflective element ofFIG. 24A;

FIG. 25B is a cross-sectional view diagram of an example embodiment ofthe slider element of the linearly translating reflective element ofFIG. 24A etched to provide sliding tabs;

FIG. 25C is a cross-sectional view diagram of an example embodiment ofthe slider element of the linearly translating reflective element ofFIG. 24B with reflective thin film deposited;

FIG. 25D is a cross-sectional view diagram of an example embodiment ofthe slider element of the linearly translating reflective element ofFIG. 24C etched to provide cavities for a slider cap;

FIG. 26 is a top view diagram of stages of fabrication of the slider capof FIG. 24B;

FIG. 27A is a top view diagram of an example embodiment of the etchedand patterned substrate of the linearly translating reflective elementof FIG. 24A;

FIG. 27B is a top and cross-sectional view diagram of an exampleembodiment of the substrate of FIG. 27A with slider element placed;

FIG. 27C is a top and cross-sectional view diagram of the substrate withslider element of FIG. 27B with slider cap placed;

FIG. 28A is a top view diagram of an example embodiment of an linearlytranslating reflective element with a rotating cylinder with areflective element patterned on the cylinder;

FIG. 28B is a side view diagram of an example embodiment of the linearlytranslating reflective element of FIG. 28A; and

FIG. 29 is a flow diagram of an example embodiment of a method ofanalyzing data of a selected portion of a wavelength spectrum.

DETAILED DESCRIPTION OF THE PREFERRED AND SELECTED ALTERNATIVEEMBODIMENTS

In describing the preferred and selected alternate embodiments of thepresent version of the invention, as illustrated in FIGS. 1-29, specificterminology is employed for the sake of clarity. The invention, however,is not intended to be limited to the specific terminology so selected,and it is to be understood that each specific element includes alltechnical equivalents that operate in a similar manner to accomplishsimilar functions.

Referring now to FIG. 1, there is illustrated a schematic illustrationof a six input fiber port by one output fiber port wavelength selectiveswitch 10. However, it is emphasized that this 6×1 embodiment isillustrated only for simplicity, and that by increasing the number ofinput fiber ports by N, then an N×1 switch 10 is contemplated herein,wherein N represents the number of input fiber ports. Preferably,wavelength selective switch 10 can be operated in either direction,wherein N of N×1 represents N input fiber ports and one output fiberport, or one input port and N output fiber ports. In the preferred 6×1wavelength selective switch 10 shown in FIG. 1, six input fiber ports12, 14, 16, 18, 20, 22, and one output fiber port 64 are opticallycoupled to fiber concentrator array (FCA) 52 (fiber port concentrator),preferably in a linear alignment, wherein preferably all-fibers(alternatively planar waveguides) 32, 34, 36, 38, 40, 42, and 46 areused to bring the respective signals of fiber ports 12, 14, 16, 18, 20,22 and 64 closer together on output face 44 of fiber concentrator 52(fiber port concentrator) adjacent the optics. Further, planarwaveguides 32, 34, 36, 38, 40, 42, 46 are also preferably used to outputthe signals in parallel in a predominantly linearly spaced grid, whereinplanar waveguides 32, 34, 36, 38, 40, 42 have curved shapes (as shown inFIG. 7) within fiber concentrator 52 and are optically coupled to inputfiber ports 12, 14, 16, 18, 20, 22. It is contemplated herein, that asignal, also known as an optical signal, may comprise multi-wavelengthWDM signals and such signals travel in free space (as beams), in fiber,in waveguides, and in other signal carriers.

Although, other coupling arrangements are possible, preferred fiberconcentrator 52 offers some additional advantages over other couplingarrangements. For example, its planar waveguides 32, 34, 36, 38, 40, 42concentrate and reduce the spacing between input fiber ports 12, 14, 16,18, 20, 22 from 125 micrometers, representative of the fiber diameters,to the considerably reduced spacing of, for example, 40 micrometers,which is more appropriate for the magnifying optics of switch 10. Eachof waveguides 32, 34, 36, 38, 40, 42 is preferably coupled to therespective 12, 14, 16, 18, 20, 22 input fiber port. Waveguides 32, 34,36, 38, 40, 42 preferably extend along a predominately common planedirecting the multi wavelength signals to output in free space and topropagate in patterns having central axis which are also co-planar.

The free-space beams output by waveguides 32, 34, 36, 38, 40, 42 offiber concentrator 52 are preferably divergent and preferably have acurved field. For simplicity, this discussion will describe all thebeams as if they are input beams, that is, output from fiberconcentrator 52 to free-space optics (FSO) 74. The beams are in fact,optical fields coupled between optical elements. As a result, the verysame principles as those discussed as input beams apply to those of thebeams that are output beams which eventually reenter fiber concentrator52 for transmission onto the network.

The beams output from fiber concentrator 52 into the free space ofwavelength selective switch 10 preferably pass through front end optics(FE) 56. Outputs of waveguides 32, 34, 36, 38, 40, 42 of face 44preferably are placed at or near the focal point of front end optics 56.Front end optics 56 preferably accepts the beams coming from or going toall fibers via input 12, 14, 16, 18, 20, 22 and output 64 fiber ports.For beams emerging from a fiber or input port, front end optics 56preferably captures, focuses, conditions, projects and/or collimates thelight in preparation for spectral dispersion by dispersive element 62.The reverse of this happens for beams converging toward a fiber; thatis, the principles of operation are identical in either case, andindependent of the direction of the light. It should be noted thatcommon dispersive elements do not operate exactly as shown in FIG. 1,more specifically the input and diffracted beams do not lie in the sameplane as shown in FIG. 1.

Although a single lens is illustrated in FIG. 1, front end optics 56 maygenerally consist of two or more lenses and/or mirrors or a combinationof the same, and may become progressively sophisticated as the demandsof wavelength selective switch 10 increases (e.g., the number of fibers,the range of wavelengths, the number of input and output fiber ports,the spacing of the MEMS mirrors, etc.). For example, in a two lens frontend optics 56, the first lens (closest to the fibers or input fiberports) may be used to produce customary flat-field and telecentric beamsthat easily accommodate simple fiber arrays or fiber concentrator 52,and the second lens may perform the majority of the collimation task (asshown in FIG. 8). As the demands on wavelength selective switch 10increases, front end optics 56 may further employ advanced features,such as aspheric optical surfaces, achromatic designs, and the like.Unlike traditional approaches wherein a separate lens must be criticallyaligned to every fiber, front end optics 56 described herein arepreferably common to every fiber, thereby enabling a realization ofsignificant savings in assembly time and cost relative to previouslyknown switch systems.

The collimated beams exiting front end optics 56 propagate substantiallywithin a common plane, and are incident upon dispersive element 62, awavelength dispersive element, wherein dispersive element 62 preferablycomprises grating lines extending perpendicular to the principal planeof wavelength selective switch 10. The beams may overlap when theystrike dispersive element 62, wherein dispersive element 62 preferablyseparates the input port beams into corresponding sets ofwavelength-separated beams, λ1 through λn (wavelengths) for each inputport, where n is the number of wavelengths in each input port.Diffraction grating 62 angularly separates the multi-wavelength inputbeams into wavelength-specific sub-beams propagating in differentdirections parallel to the principal optical plane, or alternativelyserves to recombine single-wavelength sub-beams into a multi-wavelengthbeam. Diffraction grating 62 is preferably uniform in the fiberdirection, wherein the preferred uniformity allows use of dispersiveelement 62 for beams to and from multiple input and output fibers.

The line density of dispersive element 62 should preferably be as highas possible to increase spectral dispersion, but not so high as toseverely reduce diffraction efficiency. Two serially arranged gratingswould double the spectral dispersion. However, a single grating with aline density of approximately 1000 lines/millimeter has providedsatisfactory performance. Diffraction grating 62 is preferably alignedso that the beam from front end optics 56 has an incident angle ofpreferably 54 degrees on grating 62, and the diffracted angle is about63 degrees. The difference in these angles results in opticalastigmatism, which may be compensated by placing a prism between frontend optics 56 and dispersive element 62. In brief, the diffractionefficiency of a grating is generally dependent on the characteristics ofthe polarization of the light with respect to the groove direction onthe grating, reaching upper and lower diffraction efficiency limits forlinear polarizations that are parallel p-polarization and perpendiculars-polarization to the grooves.

In addition, polarization sensitivity of the grating may be mitigated byintroducing a quarter-wave plate (not shown) after dispersive element 62or elsewhere in switch 10 whose optical axis is oriented at forty-fivedegrees to the dispersive element limiting diffraction efficiencypolarization states described previously. It is contemplated herein thatsuch quarter-wave plate may be placed elsewhere in switch 10.Preferably, every wavelength-separated sub-beam passes twice through thequarter-wave plate so that its polarization state is effectively alteredfrom input to output fiber port. That is, dispersive element 62preferably twice diffracts any wavelength-specific sub-beam, which hastwice passed through the quarter-wave plate. For example, consideringthe two limiting polarization cases the sub-beam passes once with afirst limiting polarization (for example, p-polarization) and once againwith a polarization state that is complementary to the firstpolarization state (for example, s-polarization) from the perspective ofdispersive element 62. As a result, any polarization dependenceintroduced by dispersive element 62 is canceled. That is, the netefficiency of dispersive element 62 will be the product of its S-stateand P-state polarization efficiencies, and hence independent of theactual polarization state of the input light.

In the wavelength division multiplexing (WDM) embodiments of theinvention, each input fiber port 12, 14, 16, 18, 20, 22 is preferablycapable of carrying a multi-wavelength WDM optical signal havingwavelengths λ1 through λn. Wavelength selective switch 10 is preferablycapable of switching the separate wavelength components from any inputport to planar waveguide 46 of fiber concentrator 52, which ispreferably coupled to output fiber port 64. This architecture applies aswell to a WDM reconfigurable add/drop multiplexer (ROADM), such as a 1×6ROADM in which fiber ports 12, 14, 16, 18, 20, 22 are associatedrespectively with the input (IN) (fiber port 12), five (5) DROP ports(fiber ports 14, 16, 18, 20, 22), and output (OUT) (fiber port 64). Or,in the 6×1 ROADM, input disclosed is (IN) (fiber port 12), five (5) ADDports (fiber ports 14, 16, 18, 20, 22), and output (OUT) (fiber port64). In operation, fiber ports 14, 16, 18, 20, 22, (local ports) areswitched to/from by wavelength selective switch 10, either are added(ADD) to the aggregate output (OUT) port 64 or dropped (DROP) from theaggregate input (IN) port 12.

Back end optics (BE) 66 projects the wavelength-separated beams ontobeam steering element (BSE) 68. Back end optics 66 creates the “lightbridge” between dispersive element 62 and beam steering element 68 toswitching mirror array 72. Considering the case of light diffractingfrom dispersive element 62 and traveling toward back end optics 66, suchback end optics 66 preferably captures the angularly (versus wavelength)separated beams of light, which is made plural by the number of fibers,and wherein back end optics 66 create parallel beams of light. Theparallel beams are obtained via a preferred telecentric functionality ofback end optics 66. In addition, because all beams are preferably atfocus simultaneously on the flat MEMS plane of switching mirror array72; back end optics 66 preferably performs with a field-flatteningfunctionality. After light reflects off of a MEMS mirror and back intoback end optics 66, the reverse of the above occurs; the principles ofoperation are identical in either case and are independent of thedirection of the light. Back end optics 66 preferably captures, focuses,conditions, projects and/or collimates the light in preparation forswitching by switching mirror array 72. The reverse of this happens forlight beams converging toward a fiber; that is, the principles ofoperation are identical in either case, and independent of the directionof the light.

Although a single lens is illustrated in FIG. 1, back end optics 66 maygenerally consist of two or more lenses and/or mirrors or combinationsof the same, and may become progressively more sophisticated as thedemands of wavelength selective switch 10 increase (e.g., the number offibers, the range of wavelengths, the number of input and output fiberports, the spacing of the MEMS mirrors, etc.). The focal length of backend optics 66 (or the effective focal length in the case of multiplelenses) is preferably determined from the rate of angular dispersionversus wavelength of dispersive element 62 and the desired mirrorspacing of switching mirror array 72. If the angular separation betweentwo neighboring wavelengths is denoted by A and the spacing betweentheir associated MEMS micro-mirrors is denoted by S, then the focallength of back end optics 66 (F) is approximated by F=S/tan(A). Becausethe angular dispersion of common gratings is relatively small, and/or asthe spectral separation between neighboring wavelengths is decreased,then back end optics 66 focal length may become relatively large.Preferably, however, a physically compact optical system may be retainedby providing back end optics 66 with a telephoto functionality, therebyreducing the physical length of back end optics 66 by a factor of two ormore. A three-lens system is generally sufficient to provide all of thefunctionalities described above, and the lenses themselves can becomeincreasingly sophisticated to include aspheric surfaces, achromaticdesign, etc., as the demands of wavelength selective switch 10 increase(e.g., depending on the number of fibers, the range of wavelengths, thenumber of input and output fiber port, the spacing of the MEMS mirrors,etc.). The focal length calculations set forth here with respect to theback end optics 66 are applicable to the front end optics 56 as well.

Such a preferred multi-lens back end optics 66 system, by virtue of itsincreased degrees-of-freedom, additionally allows for active opticaladjustments to correct for various lens manufacturing tolerances andoptical assembly tolerances that otherwise would not be available. Beamsteering element 68, although physically existing in the beam path ofback end optics 66, is preferably designed utilizing passive monolithicelement containing multiple prisms or lenses, as well as stacked lenses,reflective segmented prism elements and the like or combinations of thesame and preferably functions almost independently of back end optics66.

Referring now to FIG. 3A, there is illustrated a schematic illustrationof a preferred optical beam steering element included in the WSS of FIG.1 (the number of segments or facets varies with the number of signalspresent in the WSS). Beam steering element 68 preferably refractswavelength-separated beams from back end optics 66 and steers such beamsonto switching mirror array 72 based on the refractive indices of eachsegment 68.1-68.7, whether focusing all λn beams on a λn mirror ofswitching mirror array 72 or focusing some λn beams onto one mirror andother λn beams onto a linearly translating reflective element on adifferent point in space. Beam steering element 68 (or segmented prismelement, one possible type of steering element) preferably refracts λnfrom each input port 12, 14, 16, 18, 20, 22 onto λn mirror of switchingmirror array 72 (as shown in FIG. 9C) of switching mirror array 72assigned to λn. For example, preferably λ1 mirror of switching mirrorarray 72 has λ1(12)-λ1(22) from all input fiber ports 12-22 projectedonto λ1 mirror surface via beam steering element 68, and by moving,rotating or tilting λ1 mirror of MEMS switching mirror array 72,wavelength selective switch 10 preferably switches one selected λ1(12-22) from input fiber ports 12-22 to output fiber port 64 and blocksthe remaining unselected λ1(s) from input fiber ports 12-22, and soforth for λ2-λn. Each λn mirror of switching mirror array 72, in thisexample, preferably has five input beams projected simultaneously ontothe surface of such mirror, all at wavelength λn, wherein those fivebeams are preferably demultiplexed and focused by free space optics 74from input fiber ports 12, 14, 16, 18, 20 respectively. It should berecognized that utilizing beam steering element 68 enables refractingand/or steering of multiple wavelengths onto a single mirror from one ormore input fiber ports 12-22 or refracting light to any arbitrary pointrather than prior art switches, which use lenses or mirrors to focusindividual wavelengths to individual dedicated mirrors based on onefocal point. Further, it should be recognized that utilizing beamsteering element 68 enables multiple N×1 switches to be packaged as asingle unit as shown in FIGS. 14 and 15. Still further, it should berecognized that utilizing beam steering element 68 enables the potentialelimination of lenslets for each optical fiber port, thereby reducingthe number of elements and the overall cost of the switch.

Beam steering element 68 preferably is manufactured from fine-annealedglass with class-zero bubble imperfections whose facets are very finelypolished and are coated with anti-reflection material. Further, the typeof glass may be chosen to have certain optical properties at the desiredwavelengths of operation, including but not limited to opticaltransparency and refractive index. The angular deflection imparted byeach facet 68.1-68.7 of beam steering element 68 is preferably afunction of both the angle of the facet and the refractive index of theglass as shown in FIG. 3B—Beam steering Element 68 “Light DeflectionPrinciples and Equations”; hence, in principle beam steering element 68can be made from a wide variety of glass types. This allows furtheroptimization of the glass material per the criteria of cost, ease offabrication, etc. As an example, the type of glass known as BK7 is acommon high-quality, low cost glass that is preferably suitable for thisapplication.

Another criterion for glass selection may be its change in opticalproperties relative to temperature. Since the refractive index of allmaterials changes with temperature, which could in turn produceundesirable changes in the effective facet angles 102 produced by beamsteering element 68, then for demanding applications, a glass with avery low thermo-optic coefficient may be chosen at the desiredoperational temperature range. For example, the common glasses known asK5 and BAK1 have very low thermo-optic coefficients at room temperature.In addition to the precision polishing of the beam steering element 68from bulk glass, beam steering element 68 may also be fabricated usingcastable glass materials, such as sol-gel. Prism elements fabricated insuch fashion should exhibit improved performance consistency comparedwith those fabricated using traditional polishing techniques. Thematerials for fabrication of beam steering element 68 are not limited toglass but may also include high quality plastic materials such as ZEONEX(Zeon Chemicals L.P.). As such, the cost of manufacturing beam steeringelement 68 may be further lowered by using plastic injection moldingtechniques.

An alternative to fabricating beam steering element 68 from a singlemonolithic piece of glass or plastic is to fabricate each facet section,and/or groups of facet sections, individually and then vertically stackthem to create a single composite element.

In a preferred embodiment, beam steering element 68 is polished frombulk BK7 glass and has dimensions of length 40 millimeters, height 15millimeters, width at the base of 4 millimeters and width at the top of3.18 millimeters. Facet angles 102 for the six input fiber wavelengthsand one output fiber wavelength model preferably are 11.82, 8.88, 5.92,2.96, 0.00, −2.96, −5.92 degrees for each facet 68.1-68.7, respectively.For ease of fabrication so that the edges of adjacent facets arecoincident, especially with regard to fabrication by polishing, beamsteering element 68 preferably is designed to have varying degrees ofthickness for each facet, resulting in the above stated angles ofdeflection, wherein such angles of deflection preferably position thesix input λ1(12)-λ1(22) wavelengths on λ1 mirror and so on for λ2-λnmirrors. It should be noted, however, that beam steering element 68 maybe designed and manufactured having facet angles 102 different than setforth herein, depending on the fiber spacing, number of input fiberports, number of wavelength components per input port, lenses, grating,MEMS mirror configuration, and the like.

Referring again to FIG. 1, the distance between switching mirror array72, beam steering element 68, and the vertical location of the beam atbeam steering element 68, and free space optics 74 as well as otherfactors including fiber spacing, number of input fiber ports, number ofwavelength components per input port, lenses, grating, MEMS mirrorconfiguration and output fiber ports preferably determines the facetangle required to enable all six input port wavelengths to be positionedon each MEMS mirror assigned to the specific wavelength of switchingmirror array 72. Because the vertical locations of the various fiberport components are different as they intercept the beam steeringelement 68, the facet angles of beam steering element 68 preferably varyaccordingly in order to combine all of wavelengths λn at a common mirrorλn of switching mirror array 72. The analogous situation exists for theselected input port wavelength λn reflecting from mirror λn of switchingmirror array 72 directed to output fiber port 64. This is illustrated inFIG. 3B, and wherein the facet angle A can be determined from equationβ. In finding the preferred facet angle A from equation β, the knownvariables are the input beam angle, α, the distance between the inputbeam vertical location at beam steering element 68 relative to mirror λnof switching mirror array 72, y, and the distance between the beamsteering element 68 and the MEMS, z, leaving the only free variable asthe refractive index material of beam steering element 68 η. Equation βis transcendental in A and may be solved by iteration or variousalgorithms.

Referring now to FIG. 4, there is illustrated a top view of a singleaxis moveable (moveable means tilting, rotating, sliding or any othermovement resulting in a change in the angle of reflection) mirror.Switching mirror array 72 (as seen in FIGS. 1 and 2) is preferablyformed as a one-dimensional array (preferably one row of 40 mirrors) ofsingle-axis moveable mirrors, with one mirror represented by single cell(mirror) 260. Cell 260 is one of many such cells arranged typically in atwo-dimensional (one-dimensional for this embodiment) array in a bondedstructure including multiple levels of silicon and oxide layers in whatis referred to as multi-level silicon-over-insulator (SOI) structure.Cell 260 preferably includes frame 262 supported in support structure264 of switching mirror array 72. Cell 260 further includes mirror plate268 having reflective surface 270 twistably supported on frame 262 by apair of torsion beams 266 extending from frame 262 to mirror plate 268and twisting about axis 274. In one MEMS fabrication technique, theillustrated structure is integrally formed in an epitaxial (epi) layerof crystalline silicon. The process has been disclosed in U.S.Provisional Application Ser. No. 60/260,749, filed Jan. 10, 2001, (nowabandoned) is incorporated herein by reference in its entirety. However,other fabrication processes resulting in somewhat different structuresmay be used without affecting or departing from the intended scope ofthe present invention.

Mirror plate 268 is controllably tilted about axis 274 in one dimensionby a pair of electrodes 272 under mirror plate 268. Electrodes 272 aresymmetrically disposed as pairs across axis 274 respective torsion beams266. A pair of voltage signals V(A), V(B) is applied to the two mirrorelectrodes 272, while a common node voltage signal V(C) is applied toboth mirror plate 268 and frame 262.

Circumferentially lateral extending air gap 278 is preferably definedbetween frame 262 and mirror plate 268 so that mirror plate 268 canrotate with respect to frame 262 as two parts. Support structure 264,frame 262, and mirror plate 268 are driven by the common node voltageV(C), and electrodes 272 and mirror plate 268 form plates of a variablegap capacitor. Although FIG. 4 illustrates the common node voltage V(C)being connected to mirror plate 268, in practice, the electrical contactis preferably made in support structure 264 and torsion beams 266 applythe common node voltage signal to both frame 262 and mirror plate 268,which act as a top electrode. Electrical connectivity between frame 262and mirror plate 268 can be achieved through torsion beams 266themselves, through conductive leads formed on torsion beams 266, orthrough a combination of the two. Electrodes 272 are formed under mirrorplate 268 and vertical air gap 279 shown into the page is furtherdefined between electrodes 272 and mirror plate 268 and forms the gap ofthe two capacitors.

Torsion beams 266 act as twist springs attempting to restore mirrorplate 268 to its neutral position. Any potential difference appliedacross electrode 272 and mirror plate 268 exerts an attractive forceacting to overcome torsion beams 266 and to close the variable gap 279between electrodes 272 and mirror plate 268. The force is approximatelylinearly proportional to the magnitude of the applied voltage, butnon-linearities exist for large deflections. The applied voltage can bea DC drive or an AC drive per U.S. Pat. Nos. 6,543,286 and 6,705,165issued to Garverick et al. set forth below. In practice, the precisevoltages needed to achieve a particular are experimentally determined.

Because each of two electrodes 272 forms a capacitor with mirror plate268, the amount of tilt is determined by the difference of the RMSvoltages applied to the two capacitors of the pair. The tilt can becontrolled in either direction depending upon the sign of the differencebetween the two RMS voltages applied to V(A) and V(B).

It is contemplated herein that changing the angle of reflection may beaccomplished by various other means other than moving, rotating, tiltinga moveable mirror, including, but not limited to, translational motionof a fixed angled mirror, translational motion of an element withmultiple fixed angled mirrors and the like.

It is further contemplated herein that forces to accomplish movement ofthe moveable mirror or other means of reflection can be other thanelectrostatic, including, but not limited to, magnetic, thermallyactivated, piezoelectric, piezoresistant, and the like.

Referring again to FIG. 1, there are many ways of configuring the MEMSarray of micromirrors and their actuation as wavelength switchingassembly (WSA) 75. The following is an example: The MEMS array may bebonded to and have an array of solder bumps contacting it to controlcircuitry 78, preferably including high-voltage circuitry needed todrive the electrostatic actuators associated with each of the mirrors.Control circuitry (controller) 78 controls the driver circuit and hencethe mirrors in a multiplexed control system including address lines,data lines, and a clock line, driven in correspondence to an oscillator.The control is preferably performed according to pulse width modulation(PWM), a method for controlling the mirror tilt, as Garverick hasdescribed in U.S. Pat. Nos. 6,543,286, issued Apr. 8, 2003, and6,705,165, issued Mar. 16, 2004, incorporated herein by reference intheir entirety. In these methods, a high-voltage square-wave common nodedrive signal is supplied through one or more power transistors to thecommon electrical node comprising all the mirrors while the driver arraydelivers phase delayed versions of the square-wave signal to eachindividual electrode, the amount of delay determining the RMS voltageapplied across the electrostatic actuator electrodes of each mirror. Inaddition, Garverick has described in U.S. Pat. No. 6,788,981, issuedSep. 7, 2004 and incorporated herein by reference in its entirety, amethod wherein an analog control system for an array of moveablemechanical elements, such as moveable mirrors, formed in a microelectromechanical system (MEMS) is disclosed.

Control circuitry 78 preferably receives switch commands from theexternal system to effect switching of the wavelength separated channelsbetween the input and output fibers. Preferably, the drive voltage pulsewidths that correspond to mirror angles needed for switching, which isprimarily representative of the physical characteristics of the MEMSarray and its driver circuit, may be stored in an electricallyprogrammable read-only memory.

Referring to FIGS. 1 and 4, the angle of a mirror in switching mirrorarray 72 is preferably actively tilted by control circuitry 78 applyinga voltage V(A), V(B) to electrodes 272 of switching mirror array 72 sothat the selected input port sub-beam λn is preferably reflected to landprecisely at the center of concentrator waveguide 46 associated with theparticular output fiber port 64 after retracing its path through freespace optics 74. The mirror is preferably actively tilted by controlcircuitry 78 to the required angle such that the sub-beam, afterreflection off the mirror, is properly aligned to planar waveguide 46associated with output fiber port 64. Preferably, cell 260 (λ1 mirror)assigned to λ1 of switching mirror array 72 tilts its mirror plate 268,which has projected on its reflective surface 270 λ1(12)-λ1(22) from thesix input fiber ports 12-22, and by control circuitry 78 applying apredetermined voltage V(A), V(B) to electrodes 272 of switching mirrorarray 72, tilts mirror plate 268 thereby selecting λ1 from any of thesix input fiber ports 12-22 (the other λ1(s) being not selected arereflected into free space) and the selected λ1 is reflected to landprecisely at the center of planar waveguide 46 associated with outputfiber port 64 after retracing its path through free space optics 74.Wavelength selective switch 10 switches one selected λ1 from input fiberports 12-22 to output fiber port 64 and blocks the remaining unselectedλ1(s) from input fiber ports 12-22, and so forth for λ2-λn.

The described embodiment was based on 40 channels (n=40) in the˜1530-1562 nanometer band. However, the design is easily adapted toconform to various regions of the optical spectrum, including S-band,C-band, and L-band, and to comply with other wavelength grids, such asthe 100 GHz, 50 GHz, etc. grids published by InternationalTelecommunication Union (ITU).

The described design provides several advantages for facilitating itseasy insertion into WDM systems of either a few wavelengths, or fordense WDM (DWDM) systems having many wavelengths. For example, thedesign of the present invention produces lower polarization modedispersion (PMD) and low chromatic dispersion relative to previousdesigns. Low PMD and chromatic dispersion naturally follows from thefree-space optics.

Other types of MEMS mirror arrays may be used, including dual axisgimbal structure cells, those relying on flexing elements other thanaxial torsion beams, and those moving in directions other than tiltingabout a central support axis. In particular, dual axis gimbaled mirrorsfacilitate hitless switching in regards to 1×N mode of operation.Wavelength dispersive elements other than diffraction gratings also maybe used. The concentrator, although important, is not crucial to many ofthe aspects of the invention. Further, the concentrator may beimplemented in an optical chip serving other functions such asamplification, splitting or wavelength conversion.

It is contemplated in an alternate embodiment that switching mirrorarray 72 could be replaced with other optical switching elements such asliquid crystal, liquid crystals on silicon, a liquid crystal array, inkjet, mechanical, thermal, nonlinear, acousto-optic elements, amplifierand attenuators or the like known by one of ordinary skill in the art.

It is further contemplated that depending on the switching element inuse such switching element may position, configure, change, changestate, actuate, command, tilt, rotate, phase delay, or the like known byone of ordinary skill in the art.

A white-light cross connect, that is, an optical switch that switchesall λs on a given fiber together, can be adapted from the system ofFIGS. 1-5 by eliminating the dispersive element or DeMux/Mux. Althoughthe invention has been described with respect to a wavelength selectiveswitch, many of the inventive optics can be applied to white-lightoptical cross connects that do not include a wavelength dispersiveelement. Although moveable micromirrors are particularly advantageousfor the invention, there are other types of MEMS mirrors than can beelectrostatically, electrically, magnetically, thermally, or otherwiseactuated to different positions or orientations to affect the beamswitching of the invention.

Referring now to FIG. 2, a schematic illustration of a six input fiberport by one output fiber port with integrated optical switching andmonitoring system 11 is shown. Optical switching and monitoring system11 preferably includes elements and configuration of switch 10 includingsix input fiber ports 12, 14, 16, 18, 20, 22, additionally auxiliarymonitoring fiber port 23, fiber concentrator array (FCA) 52, planarwaveguides 32, 34, 36, 38, 40, 42, additionally 41, 43 and 45, FSO 74including front end optics (FE) 56, dispersive element 62, back endoptics (BE) 66, beam steering element (BSE) 68, switching mirror array72, control circuitry 78, WSA 75, output fiber port 64 and outputmonitoring fiber port 25.

According to a preferred embodiment of the invention, optical switchingand monitoring system 11 is incorporated preferably by fabricatingoutput tap 80 and planar waveguide 41 into fiber concentrator 52,whereby tap 80 preferably couples about 10% of the optical power fromoutput fiber port 64 of planar waveguide 46 into planar waveguide 41which directs the multi wavelength output beam to output in free spaceand propagate in a pattern having a central axis which is parallel withthe central axis of outputs from waveguides 32, 34, 36, 38, 40, 42 ofFIG. 1 in free space optics 74.

Alternatively, an optical switching and monitoring system with feedbackmonitoring of the output fiber may be implemented externally (off-boardof the optical switching and monitoring system 11) by fusing or splicingthe output fiber with a monitoring fiber or via use of face plateconnector and a splitter or jumper to couple about 10% of the opticalpower from output fiber port 64 fiber into monitoring fiber port 21,which is coupled to planar waveguide 41. Planar waveguide 41 outputs itsmulti-wavelength beam in free space propagating in a pattern having acentral axis which is parallel with the central axis of outputs fromwaveguides 32, 34, 36, 38, 40 in free space optics 74.

Optical switching and monitoring system 11 preferably includes auxiliarymonitoring fiber port 23 which is preferably coupled to planar waveguide43, and preferably outputs its multi-wavelength beam in free spacepropagating in a pattern having a central axis which is parallel withthe central axis of outputs from waveguides 32, 34, 36, 38, 40, 41, 42,43 in free space optics 74, thus enabling an auxiliary multi-wavelengthbeam to be monitored by optical switching and monitoring system 11. Anexternal signal not found on input fiber ports 12, 14, 16, 18, 20, 22may be input into auxiliary monitoring fiber port 23 and opticalswitching and monitoring system 11 may be utilized to monitor or readthe power of each wavelength of a multi-wavelength beam input onauxiliary monitoring fiber port 23, and to output such data to a userinterface (User i/f) port 77 shown in FIGS. 5A and 5B. It iscontemplated herein that more than one auxiliary monitoring port may beprovided in a similar fashion.

Free space optics 74 preferably position the two multi-wavelength beamsof monitoring fiber ports 21 and 23 propagating from planar waveguides42 and 43 onto monitoring mirror array 73 second row (row B). Cell 260assigned to λ1 mirror of monitoring mirror array 73 tilts its mirrorplate 268 (shown in FIG. 4), which has projected on its reflectivesurface 270 λ1(21) and λ1(23) from the two monitoring fiber ports 21 and23 and by control circuitry 78 applying a voltage V(A), V(B) toelectrodes 272 of monitoring mirror array 73 tilting mirror plate 268selects λ1 either from monitoring fiber port 21 or 23 (the other λ1being not selected is reflected away from the waveguides) and theselected λ1 is preferably reflected to land precisely at the center ofconcentrator waveguide 45 associated with the particular outputmonitoring fiber port 25 after retracing its path through free spaceoptics 74.

Optical switching and monitoring system 11 is capable of simultaneouslyswitching one selected λ1 from input fiber ports 12-22 to output fiberport 64 and blocking the remaining unselected λ1(s) from input fiberports 12-22, and so forth for λ2-λn, and switching one selected λ frommonitoring fiber ports 21 and 23 to output monitoring fiber port 25 andblocking the remaining unselected λ from monitoring fiber ports 21 or 23as well as all other λs from monitoring fiber ports 21 and 23 and soforth for λ2-λn individually. Output monitoring fiber port 25 preferablyreceives the selected single wavelength λ switched by MEMS mirror array73 (row B) after it has passed through free space optics 74. Outputmonitoring fiber port 25 preferably is coupled to optical power monitor79.

In an exemplary embodiment of optical switching and monitoring system11, MEMS mirror array 73, is replaced with a linearly translatingreflective element as provided in FIG. 24A. FIG. 24A provides WSA 75with linearly translating reflective element 2407, including sliderelement 2410. Optical switching and monitoring system 11 with linearlytranslating reflective element 2407 utilizes FSO 74 to disperse thewavelength spectrum of input monitoring fiber port 21 (shown in FIG. 1)DWDM optical signal linearly in space, so that the spectrum containingall signal wavelengths is projected horizontally across linearlytranslating reflective element 2407. Slider element 2410, which may bemoved electrostatically, comprises reflective stripe 2450 in an exampleembodiment. A non-limiting example of reflective stripe 2450 includes agold stripe, patterned as a thin film. Slider element 2410 may bepositioned across the projected spectral band containing the n incidentbeams with precision. A non-limiting example of position sensing systemis capacitive feedback, which may be implemented by controller andmemory (for example switching control circuit 71 of FIG. 5) to determinethe position of slider element 2410 along linearly translatingreflective element 2407 and correlate such position with thecorresponding optical power measured by optical power monitor 79. Forexample, n incident beams from input monitoring fiber port 21 arepositioned linearly on linearly translating reflective element 2407 byFSO 74, and depending on the linear position of slider element 2410,slider element 2410 reflects a narrow portion or narrow band of theprojected optical spectrum or selected band of the optical spectrumcontaining the n incident beams to output monitoring fiber port 25,which is coupled to optical power monitor 79. Moreover, slider element2410 may be incrementally positioned across the entire spectrum of theoptical signal to enable optical switching and monitoring system 11 tomeasure the full spectral profile of the optical signal and performanalysis of the optical signal of output monitoring fiber port 25, whichis a tapped version of the main signal of interest on output fiber 64. Amicroprocessor known to one having ordinary skill in the art may beimplemented to interpret data received by optical power monitor 79reflected from linearly translating reflective element 2407. Data mayinclude, as non-limiting examples, per-channel power, center wavelength,passband shape, optical signal-to-noise ratio (OSNR), and passbandripple. Optical switching and monitoring system 11 with WSA 75containing a moveable linearly translating reflective element 2407 inplace of monitoring MEMS mirror array 73, but without MEMS switchingmirrors 72, may be combined with a graphical interface to serve as a lowcost optical spectrum analyzer. Furthermore, linearly translatingreflective element 2407 may be combined with a switching row of MEMSmirrors 72 to implement a fully integrated optical switching andmonitoring system 11.

It is contemplated herein that linearly translating reflective element2407 may be utilized to replace MEMS mirror array 73 in FIGS. 2, 18A,19A and 21 and MEMS mirror array 72.1 in FIG. 20, offering afull-spectrum analyzing alternative to a second MEMS monitoring mirrorarray 73 of optical switching and monitoring system 11.

It is contemplated herein that linearly translating reflective element2407 may be utilized with an optical switch having one input fiber portand one or more output fiber ports (i.e. wherein the optical signalpaths in optical switching and monitoring system 11 are reversed suchthat system 11 comprises one input fiber port and one or more outputfiber ports), one or more taps 80, a combiner similar to combiner 310(shown in FIG. 5A) for combining each portion of the tapped opticalsignal from output fibers ports (such as 13, 15, 17, 19 and 21) intoinput monitoring fiber port 21.

Note that unlike the monitoring MEMS mirror array 73 in FIG. 2, thelinearly translating reflective element 2407 cannot select wavelengthsfor measurement from between multiple input ports, such as inputmonitoring fiber port 21 or input monitoring fiber port 23. Therefore,the embodiments discussed herein can include either input monitoringfiber port 21 or input monitoring fiber port 23, but not both.

Referring again to the example embodiment of FIG. 24A, linearlytranslating reflective element 2407 comprises movable slider element2410 held in place by rails 2420. Slider element 2410 may travellinearly or laterally, in a horizontal direction, under rails 2420.Slider element 2410 may include one or more thin reflective stripes 2450patterned on slider element 2410 to reflect light back through FSO 74 tophotodetector 79 in an example embodiment. Furthermore, in an exampleembodiment, 50 electrodes 2440 are used to move slider element 2410, andeach electrode has 2¹²=4095 increments of voltage for generatingelectrostatic force, allowing for precise movement of slider element2410. Sense electrodes 2444 (shown in FIG. 24B) may be used tocapacitively detect the position of slider element 2410.

Preferably, linearly translating reflective element 2407 may befabricated as part of WSA 75, on substrate 2405. A non-limiting exampleof material for substrate 2405 includes silicon. Linearly translatingreflective element 2407 may also include slider element 2410, rails2420, one or more slider electrodes 2430 and 2446, a plurality of driveelectrodes 2440, and reflective area 2450 (shown in FIG. 24B). In anexample embodiment, reflective area 2450 includes a thin gold stripe.

FIG. 24B is a cross-section perspective of linearly translatingreflective element 2407. Drive electrodes 2440 and slider electrode 2430are set on substrate 2405. Drive electrodes 2440 are covered withprotective oxide layer 2442 to prevent them from being shorted togetherby slider element 2410, which is of a conductive material. Sliderelement 2410 is placed on drive electrodes 2440 and slider electrode2430. Slider element 2410 rests loosely on substrate 2405, and is freeto slide in the dimension going into and out of the page. In an exampleembodiment, slider element 2410 is formed with V-shaped tabs 2520 (shownin FIG. 24C) on its bottom side. The tabs 2520 mate with V-shapedgrooves 2470 formed in substrate 2405 to enable slider element 2410 toslide along the channel formed by grooves 2470, into and out of the pagein FIG. 24B. Sense electrodes 2444 and second slider electrode 2446 areset in slots 2455 (shown in FIG. 24D) of slider element 2410. As withthe drive electrodes 2440, sense electrodes 2444 are covered withprotective oxide layer 2499 to prevent shorting. In an exampleembodiment, a cap is placed over the slider. The cap comprises rails2420, which rest above sense electrodes 2444 and second slider electrode2446 of slider element 2410. Rails 2420 and substrate 2405 are notattached to slider element 2410, allowing slider element 2410 to slide.However, since slider element 2410 must have a voltage imposed on it togenerate electrostatic force, it must stay in contact with eitherelectrodes 2430 or 2466, or both, while sliding. Reflective element 2450is placed on top of slider element 2410. In an example embodiment,reflective element 2450 is a thin gold stripe, deposited by thin filmdeposition methods known to those skilled in the art. Making reflectiveelement 2450 thinner will increase measurement resolution; making itthicker will increase sensitivity and measurement speed.

FIG. 24C and FIG. 24D provide bottom and top views respectively ofslider element 2410. In FIG. 24C, the bottom of slider element 2410 isshown. In an example embodiment, v-shaped tabs 2520 protrude from thebottom of slider element 2410. In FIG. 24D, the top of slider element2410 is shown. In an example embodiment, two slots 2455 are etched inslider element 2410. After slider element 2410 is assembled ontosubstrate 2405, the two slots 2455 will accept rails 2420. In an exampleembodiment, reflective material 2450 is affixed to the middle un-etchedlayer, preferentially by metal deposition.

FIG. 24E provides a top view and cross sectional view of siliconsubstrate 2460 with grooves 2470 etched in the substrate 2460. In anexample embodiment, grooves 2470 may be patterned in a v-shape. FIG. 24Fprovides a top view and cross sectional view of the electrodes patternedonto substrate 2460. In an example embodiment, slider electrode 2430 ispatterned in and around grooves 2470. A plurality of drive electrodes2440 may be placed along either or both sides of slider electrode 2430on substrate 2460. In an example embodiment, fifty drive electrodes 2440are used on either side of slider electrode 2430, and each of the fiftydrive electrodes 2440 has 4095 increments of voltage for generatingelectrostatic force, allowing precise movement of slider element 2410along slider electrode 2430. In an example embodiment, oxide layer 2442preferably covers drive electrodes 2440 to prevent the slider 2410 fromshorting electrodes, and slider electrode 2430 is left exposed so thatit can contact the slider 2410.

Other thin film metal features are also deposited on the same layer asdrive electrodes 2440 and sense electrodes 2444. Switching row electrodearray 2498 will be used to drive the MEMS switching row 72 shown in FIG.24A. Wirebond pads 2437, preferably patterned along one or more edges ofsubstrate 2460, will ultimately be used to connect WSA 75 to the rest ofoptical switching and monitoring system 11.

FIGS. 25A-D provide stages of an example embodiment of fabrication forslider element 2410. FIG. 25A provides substrate 2510. An exampleembodiment of substrate 2510 is silicon, doped for high conductivity.FIG. 25B provides tabs 2520 etched on the bottom side of substrate 2510.In an example embodiment, tabs 2520 may be etched into v-shaped tabs.Tabs 2520 may be etched using deep reactive-ion etching (DRIE). FIG. 25Cprovides reflective element 2450 patterned on substrate 2510. FIG. 25Dprovides cavities 2455 etched in substrate 2510. The etching also mayremove some of reflective element 2450 that may have overlapped the areaof either or both of cavities 2455. Slider element 2410 is now ready forsingulation.

FIG. 26 provides an example embodiment of stages of fabrication of a capthat fits in cavities (or slots) 2455 of slider element 2410 (shown inFIG. 24D). The starting material is a thin substrate 2610. Anon-limiting example of substrate 2610 is insulative silicon. Next,conductive bump pads 2640 are patterned on substrate 2610. Two innerslider electrodes 2446 are patterned from a conductive thin film(typically a metal) in long straight lines on substrate 2610. Sliderelectrodes 2446 perform the same function as slider electrode 2430 inFIGS. 24B and 24F—to contact the slider element 2410 in order to imposea voltage on it. Two outer sense electrodes 2444 may be patterned asgradually widening lines and utilized to determine the position ofslider element 2410. Oxide layer 2499 (shown in FIG. 24B) may then beadded over sense electrodes 2444 and selectively etched such that sliderelectrodes 2446 are exposed, and sense electrodes 2444 are covered withoxide layer 2499. Rectangular hole 2650 may then be etched between therails 2420 to complete the fabrication of the slider cap.

FIGS. 27A-C provide an example embodiment of the stages of the assemblyprocess for WSA 75 containing a moveable reflective element in place ofmonitoring MEMS mirror Array 73. FIG. 27A provides etched substrate 2460with patterned electrodes in place, as shown in FIG. 24F. In an exampleembodiment, one or more driver chips 2710 are placed on substrate 2460by one of several well-known flip-chip processes. In an alternativeprocess, driver chips 2710 may be placed last in the assembly, afterlinearly translating reflective element 2407 cap and slider, as well asthe switching row MEMS mirrors have been attached. Driver chips 2710 mayinclude, as non-limiting examples, a general purpose processor, amicroprocessor, a digital signal processor, an application specificintegrated circuit (ASIC) having appropriate combinational logic gates,a programmable gate array (PGA), a field programmable gate array (FPGA),an array of high voltage operational amplifiers, an array of highvoltage level shifters, an array of digital to analog converters (DACs),a memory device (RAM or ROM), a contents addressable memory (CAM)device, various combinations of these, and the like. It is contemplatedherein that various MEMS array control electronics described in U.S.Pat. Nos. 6,543,286, 6,705,165, 6,788,981, and 6,961,257 describeseveral possible non-limiting embodiments of driver chips 2710 and areincorporated herein by reference in their entirety. Although thedescriptions of embodiments in these reference patents are generallydirected toward electrostatic control of micromirrors, they are alsowell suited to drive linearly translating reflective element 2407. Thesame electronics devices may be used to drive both the mirrors inswitching mirror row 72 and linearly translating reflective element2407.

FIG. 27B provides a top view and cross-sectional view of the placing ofthe slider element. Slider element 2410 is placed in grooves 2470, thegrooves etched into substrate 2460. FIG. 27C provides a top view andcross-sectional view of the placing of the cap element. Cap element 2745is placed over slider element 2410. In an example embodiment cap element2745 may be attached with non-conductive paste (NCP) and stud bumps.Also at this stage of the exemplary embodiment, switching row MEMSmirror array 72 may also be attached over its electrode array 2498,using a process similar to that used for cap element 2745. In analternative exemplary embodiment, cap element 2745 and the switching rowMEMS mirror array 72 may be fabricated in a single piece of, forexample, silicon, and attached as one unit.

As can be seen in either FIG. 24A or FIG. 27C, slider element 2410 isheld in place by grooves 2470 and rails 2420. Slider element 2410 isfree to slide horizontally left and right. When an electrical potentialdifference exists between slider element 2410 and any of driveelectrodes 2440, an electrostatic force is set up between the two.Because of charge redistribution in the conductive slider element 2410and drive electrodes 2440, this force is always attractive. Driver chips2710 impose voltage on slider element 2410 via slider electrodes 2430and 2446. Such electrodes then impose a different voltage onto selecteddrive electrodes 2440, resulting in attractive force on the slider 2410.Stimulating drive electrodes 2440 underneath slider 2410 with apotential different than that of slider element 2410, will cause sliderelement 2410 to be held in place. Stimulating drive electrodes 2440 justto the right of slider element 2410 with a voltage different from thatof slider element 2410, while stimulating electrodes directly under theslider with a potential the same as slider element 2410 (thus cancelingthe force holding it in place), will cause slider element 2410 to bepulled to the right. The same principle can move slider element 2710 tothe left, when drive electrodes 2440 to the left is stimulated. Bystimulating electrodes 2440 left, right, and under slider element 2410to create different amounts of potential difference left, right, andunder, force balances can be set up to move the slider at very preciseincrements left or right, or stop it at a precise location.

Recall from FIG. 2 that the monitoring input of optical switch andmonitor system 11 projects the optical spectrum to be monitored as ahorizontal line (going into the page of FIG. 2), which coincides withthe travel path of reflective stripe 2450 on slider element 2410. Asslider element 2410 moves along its path, it reflects a thin portion ofthe optical spectrum back to the photodetector 79 of optical switch andmonitor system 11. When a system processor correlates the powermeasurement obtained by photodetector 79 with the position of sliderelement 2410 for a number of linear locations on the spectrum, adetailed measurement of the spectrum is obtained, and can be presentednumerically or graphically to a user and/or a higher level processor, orcan be stored in a memory. This is the same principle used in manyoptical spectrum analyzers: mechanically sweeping a narrow, movingmeasurement window across the spectrum, measuring power at eachincrement of movement, and plotting the results. Utilizing softwarealgorithms known to those skilled in the art, the data obtained in thespectral sweep can be used to calculate passband size and shape, centerwavelength, average power, and signal to noise ratio of the signalsfound in the wavelength spectrum of interest.

Note that the controller or driver chips 2710 may sweep slider element2410 across the entire spectrum, or any desired portion of the spectrumthat is of interest. The controller can also make tradeoffs between thespeed of the sweep and the accuracy of the measurement. Sweep time,direction, length, and sweep frequency can be changed as desired by thecontroller to address the needs of the system making the measurement.

Note too that slider element 2410 can measure power at any point on thespectrum of interest. It is not confined to discrete windows aroundcertain wavelengths (for example, ITU wavelengths); as is themeasurement system based on monitoring mirror row 73 in FIG. 2.

In order to obtain an accurate spectral picture, slider element 2410precise position across the horizontal line of translation must be knownby controller or driver chips 2710 or processor, so that it can becorrelated to a wavelength “position” on the optical spectrum. Thecorrelation between slider element 2410 position and wavelengthmeasurement window can be determined to first order by design, andimproved by factory calibration with known standard wavelengths, ifdesired. Driver chips 2710 can measure the slider's element 2410position by determining the capacitance between slider element 2410 andthe sense electrodes 2444. The gradually tapering sense electrodes 2444shown in FIG. 26 are one example of a sense electrode geometry that canbe used by those skilled in the art to determine slider location.Because of the tapered shape of the sense electrodes 2444, thecapacitance between them and slider element 2410 will have a uniquevalue when slider element 2410 is overlapping sense electrodes 2444 at agiven location on the horizontal axis. Alternatively, those skilled inthe art will see other methods of placing sense electrodes, including bynot limited to: interspersing sense electrodes with the driveelectrodes, using different electrode geometries, and/or using differentnumbers of electrodes, and combining sense and drive on the sameelectrodes.

In an alternate exemplary embodiment of optical switching and monitoringsystem 11, monitoring MEMS mirror array 73, is replaced with a moveablereflective element as provided in FIG. 28A-B. FIG. 28A provides a topview of a portion of the system shown in FIG. 2, consisting of theportion between the BSE (or segmented prism element (SPE)) 68 and theWSA 75. Added to the system in FIG. 2 are a blocker structure 2840 witha slit 2845 and moveable reflective element 2800 comprising a steppermotor 2810 and a patterned rotating cylinder 2830. Patterned rotatingcylinder 2830 utilizes FSO 74 to project spatially input monitoringfiber port 21's DWDM optical signal as a band of n incident beams(wavelengths) linearly positioned across slit 2845 and patternedrotating cylinder 2830. Moveable reflective element 2800, a non-MEMScylinder with a reflective spiral 2825 patterned on cylinder 2830, isused to reflect a selected portion of the desired optical spectrum ofinput monitoring fiber port 21 optical signal to output monitoring fiberport 25. Preferably, reflective spiral 2825 may be patterned onto adark, light absorbing cylinder 2830 as a spiral. A stepper motor 2810may rotate the cylinder behind slit 2845, causing a small portion ofreflective spiral 2825 element to appear to move linearly or laterallywhen viewed through the slit. In an example embodiment, optical powerreflected back to output monitoring fiber port 25 by reflective spiral2825 may be recorded using a photodetector 79 and correlated to cylinder2830 (and hence reflectively spiral 2825) position along the horizontalaxis of moveable reflective element 2800. FSO 74 may capture a reflectedbeam from moveable reflective element 2800 and carry the beam throughfree-space to a connecting fiber, output monitoring fiber port 25, andleading to photodetector 79. A processor may calculate power,wavelength, passband shape, OSNR, etc., in the same manner as describedabove for linearly translating reflective element 2407 of FIG. 24-27.

FIG. 28A provides a top view of the patterned cylinder embodiment.Moveable reflective element 2800 is mounted on baseplate 2860, which isthe same as the baseplate shown in FIGS. 1 and 2, and is made, forexample, of glass. A wavelength switching array (WSA), similar to WSA 75in FIG. 2, including array of switching row MEMS mirror array 72 (2820)but not including array of monitoring mirrors 73 may be placed onbaseplate 2860. Cylinder 2830 is placed in front of the WSA 75.Reflective strip 2825 is patterned onto the otherwise light-absorbingcylinder 2830, for example, in a spiral pattern. A non-limiting exampleof reflective strip 2825 is a thin gold stripe. In an exampleembodiment, stepper motor 2810 rotates cylinder 2830 such that a smallportion of reflective strip 2825 moves linearly across cylinder 2830when viewed length-wise along cylinder 2830 through slit 2845. A blockerstructure 2840 with slit 2845 may be positioned in front of cylinder2830, opposite the WSA 75. Beam steering element 2850 (68) may be placedon baseplate 2860 in front of blocker structure 2840. FIG. 28B providesa head-on view of moveable reflective element 2800, as would be seen bylight beams entering the system (that is, as would be seen by anobserver standing on baseplate 2860 of FIG. 2, just right of the BSE2850 (68), and looking right into blocker 2840 through slit 2845).Cylinder 2830 is rotated via stepper motor 2810 and as cylinder 2830turns, reflective element 2825 appears to move linearly across slit2845.

As in linearly translating reflective element 2407 of FIG. 24, it isnecessary to know the precise position of cylinder 2830 for eachincremental power measurement. This can be accomplished by monitoringthe rotational position of stepper motor 2810 by keeping track ofcommands sent to it from motor control electronics (not shown in thefigure). In general, stepper motor controllers can control motor shaftangle to very high precision.

It is contemplated herein that moveable reflective element 2800 may beutilized to replace MEMS mirror array 73 in FIGS. 2, 18A, 19A and 21 andMEMS mirror array 72.1 in FIG. 20, offering a full-spectrum analyzingalternative to a second MEMS monitoring mirror array 73.

FIG. 29 provides a flow diagram of an example embodiment of method 2900of analyzing data of a selected portion of a wavelength spectrum. Inblock 2910, a wavelength spectrum is received. “Received” in thiscontext refers to the conditioning, focusing, magnifying, dispersion,and projection of the spectrum as performed by the shared front endoptics 56, wavelength dispersive element 62, beam steering element 68,and backend optics 66 described in for example FIG. 2 and elsewhereherein. In general, the optical spectrum projected horizontally acrossthe path of moveable reflective elements 2407 or 2800 is identical tothat projected across MEMS mirror row 73 in FIGS. 1 and 2. In block2920, moveable reflective element 2800 or 2407 is positioned to reflecta selected portion of the wavelength spectrum. In block 2930, thedesired region of the reflected portion of the wavelength spectrum isscanned. In block 2940, data obtained from the scan is used to obtain aspectral graph of the signal, as well as calculate parameters ofinterest such as center wavelength, passband, passband ripple, and OSNRdata. In an example embodiment, spectral regions between wavelengths maybe measured to obtain background noise readings and to obtainsignal-to-noise ratio data. In another example embodiment, the moveablereflective element 2800 or 2407 may be moved to an arbitrary location bya controller or processor and to be held there, allowing real-timedynamic measurement of a desired narrow band of the spectrum.

Referring again to FIG. 2, power monitor (optical measurement device) 79preferably is a photodiode, preferably measuring the power level ofwavelength λn switched by monitoring mirror array 73 (row B), measuringone wavelength at a time. As monitoring mirror array 73 (row B) selectswavelength λn and routes it to waveguide 45 coupled to output monitoringfiber port 25, power monitor 79 preferably measures the power of suchwavelength λn. Alternatively, power monitor 79 may be any type ofoptical measuring device, for example a device capable of measuringpower of one or more wavelengths by scanning the multi-wavelengthcomponents, determining signal to noise ratios by spectrum analyzing thewavelength bandwidth, measuring polarization-dependent properties, andthe like. The optical intensities for all wavelength-separated signalsare preferably converted to analog or digital form by power monitor 79and supplied to control circuitry 78, which preferably adjusts switchingmirror array 72 as set forth herein to adjust the power of wavelength λnto conform to one or more predetermined criteria.

Other forms of power monitoring are possible as long as the timenecessary for resolutions of differences in wavelength channel powerlevels is sufficient for power adjustments. If the adjustments areintended to only address aging and environmental effects, the resolvedmeasurement time may be relatively long. On the other hand, fastfeedback may be necessary for initializing switch states, forcompensating for transient changes in power level such as occur from thecombination of polarization-dependent loss and polarization fluctuationswhich vary at the wavelength level, for stabilizing against vibration,and for alarm signaling to protection circuitry and for network faultrecovery. Moreover, by replacing photodetector 79 with othercommercially available devices, other parameters may be measured such asoptical signal to noise ratio (OSNR), center wavelength, transientbehavior, or bit error rate.

Moreover, various configurations of optical switching and monitoringsystem 11 are contemplated herein, including taps or splitters for allor a selected number of input and output fiber ports, including theirassociated planar waveguide, free space optics, MEMS mirrors and thelike.

Referring now to FIG. 5A, a functional block diagram of a one input portby five output fiber port 1×N (N=5) optical switching and monitoringsystem 10.1 wavelength selective switch with power monitor and feedbackcontrol is illustrated according to an alternate embodiment of thepresent invention. In optical switching and monitoring system 10.1,forty wavelengths enter input port (In) 12 and are demultiplexed (DeMux)302 into forty separate wavelengths λ1-λ40, the optical cross-connect(OXC) 304 switches the forty wavelengths, multiplexes (Mux) 306, andoutputs the forty wavelengths to their switch selected output (Out 1-5)13, 15, 17, 19, 21. Forty wavelengths in and forty wavelengths out;however, the forty wavelengths out are distributed across the outputfiber ports (Out 1-5) 13, 15, 17, 19, 21 as selected by the opticalcross-connect switch 304. About 10% of the optical power of each output(Out 1-5) 13, 15, 17, 19, 21 is tapped or split off (Output taps) 308 toa 5:1 combiner 310, which is coupled to an 80 channel selector 312.Channel selector 312 preferably selects one wavelength of the fortyinternal or forty external (Aux. OPM In) 23 and feeds such wavelength tothe photo diode (PD) 314. The output from the photodiode is passed tothe equalization control circuit 316 and/or to user interface 77 (Useri/f). The equalization control circuit 316 preferably controls the perwavelength variable optical attenuator (VOA) 318 which adjusts thewavelength transmitted power to conform to one or more predeterminedcriteria. Switch commands 71 are provided for an external controller,via user interface 77, for wavelength selection from input to outputswitching, for wavelength selection for power monitoring, and/or powermonitoring.

Referring now to FIG. 5B, a functional block diagram of five input fiberports by one output fiber port N×1 (N=5) optical switching andmonitoring system 10.2 wavelength selective switch with power monitorand feedback control is illustrated according to preferred embodiment ofthe present invention. In optical switching and monitoring system 10.2,forty wavelengths enter each input port (In 1-5) 12, 14, 16, 18, and aredemultiplexed (DeMux) 302 into five sets of forty separate wavelengthsλ1-λ40, the optical cross-connect (OXC) 304 selects and switches fortywavelengths, multiplexes (Mux) 306 and outputs forty selectedwavelengths to output (Out) 64. About 10% of the optical power of output(Out) 64 is tapped or split off (Output Tap 308) to an 80 channelselector 312. The channel selector 312 selects one wavelength of theforty internal or forty external (Aux. OPM In) 23 and feeds suchwavelength to the photo diode (PD) 314. The output from the photodiodeis passed to the equalization control circuit 316 and/or to userinterface 77 (User i/f). The equalization control circuit 316 controlsthe corresponding wavelength variable optical attenuator (VOA) 318 whichadjusts the transmitted power to conform to one or more predeterminedcriteria. Switch commands 71 are provided from an external controller,via user interface 77, for wavelength selection from input to outputswitching, for wavelength selection for power monitoring, and/or forpower monitoring.

User interface 77 preferably is an interface enabling information topass from the optical switching and monitoring system to outside of theoptical switching and monitoring system, and from outside the opticalswitching and monitoring system into the optical switching andmonitoring system, wherein such outside systems include but are notlimited to a human operator, an embedded controller, network managementsystems and/or network alarming systems. Information may include, but isnot limited to, wavelength routing information, wavelength selection forpower monitoring, wavelength to be switched from input to output, switchstatus, wavelength power levels, wavelength power level settings, andthe like.

The optical monitoring system described above in FIGS. 2 and 5 ispreferably internal to the optical switching and monitoring system andhas the advantage of using all the free space optics and MEMS mirrors ofsuch switch. However, an external optical monitoring system is possiblewherein photodiode 79 is external and coupled to the optical switchingand monitoring system via monitoring fiber 25 (shown in FIG. 2), withthe advantage of monitoring all the output signals of the switch.

Per-wavelength power adjustment is achieved in the embodiment of FIG. 1with relatively minor additions to the hardware other than the opticalpower monitor and taps shown in FIGS. 2 and 5. Mirrors 72 used forswitching between channels and for optimizing transmission are usedadditionally for the variable attenuation of the output power, therebyeffecting per-wavelength variable transmission through optical switchingand monitoring system 11. To achieve such variable attenuation externalto the switch would otherwise require separate attenuators in each ofthe multiple wavelengths of each of the optical channels. Moreover, thecontrol functions can be incorporated into the same control circuitry78.

There are two principal types of misalignment or mismatch between thebeam and waveguide to attain variable attenuation of the wavelengthoutput power. Referring now to FIG. 6A, a cross sectional viewillustrates a mismatch in optically coupling a wavelength component beam110 to the waveguide substrate 52 according to a preferred embodiment ofthe present invention. Positional mismatch occurs when, as illustratedin the cross-sectional view of FIG. 6A, central axis 112 of wavelengthλn beam 110 is offset slightly from central axis 114 of waveguide 116 offiber concentrator 52. The figure, being suggestive only, does notillustrate the smooth variation of the optical fields both inside andoutside of the illustrated wavelength λn beam 110 and waveguide 116 andacross the lateral interface. FIG. 6A further assumes that the two modalfields have the same width, which is the typical object of opticaldesign. Slightly tilting mirror λn of switching mirror array 72 (row A)to deliberately misalign or mismatch wavelength λn beam 110 entry intowaveguide 116 of fiber concentrator 52, results in a degraded couplingand in loss of wavelength λn beam 110 optical power in waveguide 116. Ina typical embodiment, coupling is attenuated by about 1 dB permicrometer of positional mismatch.

On the other hand, angular mismatch occurs when, as illustrated in thecross-sectional view of FIG. 6B, wavelength λn beam 110 is angularlyinclined with respect to waveguide 116 even if their central axes 112and 114 cross at their interface 118. Angular mismatch degrades thecoupling because a phase mismatch occurs between the two fields at theinterface arising from the axial z-dependence of the two complex fields.In a typical embodiment, coupling is degraded by about 1 dB per degreeof angular offset but the angular dependence depends strongly upon theoptics. It should be appreciated that a beam can be both positionallyand angularly mismatched with a waveguide. It should be yet furtherappreciated that the mismatch can occur at the transition from freespace to fiber (if no concentrator) and its beam field defined by therest of the optical system.

Referring now to FIG. 7A, there is illustrated a fiber concentrator 120that utilizes the optical fiber included in the switch of FIGS. 1, 2 and5 to bring optical signals closer together. Fiber holder 122 ispatterned by precision photolithographic techniques with a series ofpreferably V-shaped grooves (or other channel configuration) in thegeneral planar pattern shown in fiber holder 122 of FIG. 7A. Single-modeor multi-mode optical fibers 124 having cores 126 surrounded bycladdings 127 and buffer 128. In this application, optical fibers 124are stripped of their protective buffer 128 and cladding 127, or havetheir cladding 127 reduced or tapered toward output face 44 of fiberholder 122 to enable close linear placement of cores 126. Typical coreand cladding diameters are respectively 8.2 micrometers and 125micrometers. Among other favorable attributes, the concentrated fibercore spacing reduces the amount of “dead space” between fibers whichwould otherwise increase the total mirror tilt range. Tapered fibers 124are preferably placed into the grooves with their tapered ends formingtransition to free-space optics 74. The all-fiber design eliminates thetedious alignment and in-path epoxy joint of combination waveguides, asshown in FIGS. 7B and 7C. The design also eliminatespolarization-related effects arising in planar waveguides.

Fiber concentrator 120 interfaces widely separated optical fibers 124with the closely configured free space optics 74 and wavelengthswitching assembly 75 of WSS of FIGS. 1 and 2. Multiple fibers 124 aretypically bundled in a planar ribbon. V-shaped grooves in fiber holder122 hold the reduced cladding 128 with a spacing of, for example, 40micrometers. Although a core of each fiber 124 has a relatively smallsize of about 8 micrometers, its outer glass cladding results in a fiberdiameter of approximately 125 micrometers. The large number of fibers,which can be handled by the single set of free-space optics 74 of theinvention, arranged along an optical axis make it difficult to process alarge number of fiber signals with such a large spacing between thembecause the outermost fiber signals are so far from the optical axiscapabilities of the mirrors. Also, as discussed in more detail below, asignificant amount of optical magnification is required between thesefibers and the MEMS mirror array, and the MEMS design and function isgreatly simplified as a result of concentrating the fiber spacing.

Referring now to FIG. 7B, a schematically illustrated optical fiberconcentrator array 52, using planar waveguide included in the 5×1 WSSaccording to a preferred embodiment of the present invention, andincluded in the switch of FIGS. 1, 2 and 5B. Single-mode optical fibers124 having cores 126 surrounded by claddings 127 (shown in FIG. 7A) arebutt coupled to fiber concentrator 52. In the 6×1 switch 10 shown inFIG. 1, six input fiber ports 12, 14, 16, 18, 20, 22 and output fiber 64are preferably optically coupled to fiber concentrator 52 in a linearalignment and are preferably optically coupled to input fiber ports12-22 and output fiber 64 to bring their signals closer together onoutput face 44 of fiber concentrator 52 adjacent the optics, and tooutput the beams in parallel in a linearly spaced grid. Returning toFIG. 7B, fiber concentrator 52 preferably has curved shaped planarwaveguides 32, 34, 36, 38, 40 and 45 corresponding to input fiber ports12, 14, 16, 18, 20, and output fiber 64 within fiber concentrator 52 topreferably concentrate and reduce the spacing between fiber input fiberports 12, 14, 16, 18, 20, 64 from 125 micrometers, representative of thefiber diameters, to the considerably reduced spacing of, for example 30or 40, micrometers and preferably no more than 50 micrometers which ismore appropriate for the magnifying optics of switch 10 and an optimumtilt range of the mirrors. Each of waveguides 32, 34, 36, 38, 40, and 45is preferably coupled to respective 12, 14, 16, 18, 20 input port andoutput fiber 64. Further, waveguides 32, 34, 36, 38, 40, 41 and 45preferably extend along a common plane directing the wavelengths tooutput in free space and to propagate in patterns having central axeswhich are also preferably co-planar.

FIG. 7B further discloses the fabricating of output tap 80 and planarwaveguide 41 into fiber concentrator 52, whereby tap 80 preferablycouples about 10% of the optical power from output fiber port 64 ofplanar waveguide 45 into planar waveguide 41, which directs the multiwavelength output beam to output in free space and to propagate in apattern having a central axis which is preferably co-planar with outputsfrom waveguides 32, 34, 36, 38, 40, 45 of FIG. 2 in free space andswitched by monitoring mirror array 73 (row B) after it has passedthrough free space optics 74.

Fiber concentrator 52 in FIG. 2, may include auxiliary monitoring fiberport 23, coupled to planar waveguide 43, wherein fiber concentrator 52preferably outputs its multi-wavelength beam in free space propagatingin a pattern having a central axis which is preferably co-planar withoutputs from waveguides 32, 34, 36, 38, 40, 41 in free space optics 74,thereby enabling an external multi-wavelength beam to be monitored byoptical switching and monitoring system 11. An external signal not foundon input port 12, 14, 16, 18, 20, 22 may be input into auxiliarymonitoring fiber port 23 and optical switching and monitoring system 11may be utilized to monitor or read the power of each wavelength of amulti-wavelength beam on auxiliary monitoring fiber port 23 and tooutput such data to a user interface (User i/f) 77 port shown in FIGS.5A and 5B. It is contemplated herein that additional auxiliarymonitoring fiber port 23 may be added in a similar fashion.

Potential limitations on the free space optics 74 and wavelengthswitching assembly 75 occur when configuring larger numbers of fibersthan the present invention, if arranged along an optical axis of inputfiber ports 12, 14, 16, 18, 20 and output fiber 64. Absent a fiberconcentrator 52, adding additional fibers makes it difficult to switchsuch increased number of fiber signals with such a large spacing betweensuch fibers because the outermost beams are so far off the centeroptical axis capabilities of the mirrors in the preferred embodimentbetween input fiber ports 16 and 18. Also, as discussed in more detailbelow, a significant amount of optical magnification is required betweenthese fibers and the MEMS mirror array, and the MEMS design and functionare greatly simplified as a result of concentrating the fiber spacing.

Referring now to FIG. 7C, a schematically illustrated opticalconcentrator array 53 is shown wherein planar waveguides are included inthe 1×5 WSS according to an alternate embodiment of the presentinvention. Single-mode optical fibers 124 having cores 126 surrounded bycladdings 127 and buffers 128 (shown in FIG. 7A) are butt coupled toconcentrator 53. Illustrated in the 1×5 wavelength selective switch 10.1shown in FIG. 5A, one input port 12 and five output fiber ports 13, 15,17, 19, 21 are preferably optically coupled to fiber concentrator 53 ina linear alignment and are preferably optically coupled to fiber inputport 12, and output fiber ports 13-21 to bring their beams closertogether on output face 44 of fiber concentrator array 53 adjacent theoptics, and to output the beams in parallel in a linearly spaced grid.Fiber concentrator 53 preferably has curved shaped planar waveguides 32,33, 35, 37, 39, 47 and 49 within fiber concentrator 53 to preferablyconcentrate and reduce the spacing between fiber input fiber ports 12,13, 15, 17, 19, 21 from 125 micrometers, representative of the fiberdiameters, to the considerably reduced spacing of, for example, 30 or 40micrometers and preferably no more than 50 micrometers which is moreappropriate for the magnifying optics of switch 11 and an optimum sizeand spacing of the mirrors. Each of waveguides 32, 33, 35, 37, 39, 47 ispreferably coupled to the respective input fiber port 12, and outputfiber ports 13, 15, 17, 19, 21. Further, waveguides 32, 33, 35, 37, 39,47 preferably extend along a common plane directing the multi wavelengthbeams to output in free space and to propagate in patterns havingcentral axes which are also preferably co-planar.

FIG. 7C further discloses the fabricating of output taps 80 and planarwaveguide 49 into fiber concentrator 53 whereby taps 80 preferablycouple about 10% of the optical power from output fiber ports 13, 15,17, 19, 21 via waveguides 33, 35, 37, 39, 47 into planar waveguide 49,which directs the multi wavelength output beam to output in free spaceand to propagate in a pattern having a central axis which is preferablyco-planar with outputs from waveguides 32, 33, 35, 37, 39, 47 in freespace and switched by monitoring mirror array 73 (row B) after it haspassed through free space optics 74. The reflected beam preferablypasses again through free space optics 74 and into output waveguide 45(shown in FIG. 2 but not in FIG. 7C) which guides the signal tophotodetector 79 wherein fiber concentrator 53 performs the functions oftaps 308 and 5:1 combiner 310 in FIG. 5A.

Concentrator 53 may also include auxiliary monitoring fiber port 23,coupled to planar waveguide 43 wherein fiber concentrator 53 preferablyoutputs its multi-wavelength beam in free space propagating in a patternhaving a central axis which is preferably co-planar with outputs fromwaveguides 32, 33, 35, 37, 39, 47 in free space optics 74, therebyenabling an external multi-wavelength beam to be monitored by opticalswitching and monitoring system 10.1 or 11. An external signal not foundon input (N) may be input into auxiliary monitoring fiber port 23 andoptical switching and monitoring system 10.1 or 11 may be utilized tomonitor or read the power of each wavelength of a multi-wavelength beamon auxiliary monitoring fiber port 23 and to output such data to a userinterface (User i/f) port shown in FIGS. 5A and 5B. It is contemplatedherein that additional auxiliary monitoring fiber port 23 may be addedin a similar fashion.

Fiber concentrators 52 and 53 can be easily formed by a conventional ionexchange technique, such as is available from fiber array manufactures,such as WaveSplitter Technologies of Fremont, Calif. For example,waveguides 32, 34, 36, 38, 40, 41, 45, 33, 35, 37, 39, 47, 49 are formedby doping such signal path to obtain a higher refractive index than thesurrounding undoped glass, and thus, can serve as optical waveguides.However, a half-elliptical shape is optically disadvantageous.Therefore, after completion of ion exchange, a vertical electric fieldis applied to the substrate to draw the positive ions into the glasssubstrate to create nearly circular doped regions. These serve as theplanar optical waveguides surrounded on all sides by the lower-indexglass. Other methods are available for forming planar waveguides.

Fibers 124 of FIGS. 7B and 7C are aligned to fiber concentrators 52 and53 at input face 127 of fiber concentrators 52 and 53. Preferably, thefiber end faces are inclined by about 8 degrees to the waveguides inorder to virtually eliminate back reflections onto fibers 124. Othertypes of concentrator chips and fiber holder substrates are availableand are contemplated herein.

Fiber concentrators 52 and 53 preferably create a relatively narrowspread of parallel free-space beams in a linear arrangement forwavelength selective switch 10 and 11, as Golub et al. has described inU.S. Pat. No. 6,694,073, issued Feb. 17, 2004. Even when multiple fibersare connected to wavelength selective switch 10 and 11, the fibers areconcentrated to an overall width of only about 1 millimeter. The designallows shorter focal length lenses and significantly reduces the overallsize of the package. It is also more reliable and highly tolerant toenvironmental stress than previously described systems. Without aconcentrator, the number of fibers connected to wavelength selectiveswitch 10 and 11 would be limited for a given package size.

An example of front end optics 56 is illustrated in more detail in thecross-sectional view of FIG. 8, as Golub has described in U.S. Pat. No.6,694,073, issued Feb. 17, 2004. The free-space beams output by thewaveguides, whether planar or fiber, of fiber concentrator 52 or 53 aredivergent and form a curved field. This discussion will describe all thebeams as if they are input beams, that is, output from the concentratorin to the free-space optics. The beams are in fact optical fieldscoupled between optical elements. As a result, the very same principlesapply to those of the beams that are output beams which eventuallyreenter fiber concentrator 52 or 53 for transmission onto the network.

The beam output from fiber concentrator 52 or 53 enters into thewavelength selective switch through field-flattening lens 220, in orderto flatten what would otherwise be a curved focal plane of thecollimator lens. Field-flattening lens 220 accepts a flat focal planefor the multiple parallel beams emitted from the concentrator. In thereverse direction, field-flattening lens 220 produces a flat focal planeand parallel beams compatible with the end of the concentrator 42 toassure good coupling to waveguides in the concentrator.

In many optical systems, an image is formed on a curved, non-planarsurface, typically by beams non-parallel to each other. In manyapplications such as photographic imaging systems, such minor deviationsfrom a flat field are mostly unnoticeable and inconsequential. However,for a wavelength selective switch based on free-space optics, parallelsingle-mode fibers, small parallel beams, and planar mirror arrays, acurved image can degrade coupling efficiency. Performance is greatlyimproved if the optics produce a flat focal plane at output face 44, andon the return trip it will be imaged onto fiber concentrator 52 or 53waveguide ends. Hence, the ends of the input waveguides in fiberconcentrator 52 or 53 are imaged onto the ends of the output waveguidesin fiber concentrator 52 or 53, and the efficiency of coupling into thesingle-mode waveguides strongly depends on the quality of the image.Without the field-flattening lens, it would be very difficult to build aWSS with more than a few fiber ports because the error in focus wouldsignificantly increase for fibers displaced away from the optical axis.Field-flattening lens 220 preferably is designed as an optical elementwith negative focal length, and is thicker at its periphery than at itsoptical axis in the center. The basic function of the thicker glass atthe periphery is to delay the focus of the beams passing therein. Thedelayed focus serves to create a flat plane of focus points for allbeams, rather than a curved plane of foci that would occur otherwise. Afield-flattening lens may be implemented as a singlet lens, a doublet,aspheric, or other lens configuration.

A field-flattening lens may, in the absence of further constraints,produce an optical field in which the off-axis beams approach the flatfocal plane at angles that increasingly deviate from normal away fromthe optical axis. Such non-perpendicular incidence degrades opticalcoupling to fibers arranged perpendicular to the flat focal plane.Therefore, performance can be further improved if the beams are made toapproach the focal plane in parallel and in a direction normal to theflat focal plane. This effect of producing parallel beams is referred toas telecentricity, which is aided by long focal lengths.

After field-flattening lens 220, the beams pass through a collimatingdoublet lens 222, preferably consisting of concave lens 224 joined toconvex lens 226. Doublet lens 222 may be a standard lens such as ModelLAI-003, available from Melles Griot, which offers superior collimatingand off-axis performance. The effective focal length of the assembly maybe about 14 mm. Collimating lens 222 is illustrated as following thefield-flattening lens 220, which is preferred, but their positions canbe reversed with little change in performance.

As an aid to reducing the overall insertion loss of the integrated WSSin FIGS. 1, 2, 4, 5 (although not a strict requirement), prism 228,which may be a simple wedge, preferably is placed between collimatinglens 222 and dispersive element 62. Prism 228 pre-corrects for theastigmatism introduced by dispersive element 62. The wedge angle of theprism, along with the type of glass from which it is made, allowselliptically shaped (or astigmatic) beams to be created. If prism 228 iscomposed of common optical glass, the wedge angle is typically on theorder of 25 degrees to compensate for the type of dispersive element 62considered for the invention. The ellipticity counteracts a similarellipticity that is an undesirable by-product of dispersive elements.The net result of the prism and grating is a distortion-free opticalbeam that can be efficiently processed by the remaining opticalcomponents in the system and ultimately coupled with high efficiencyback into the small core of a single-mode fiber. Field-flattening lens220, collimating doublet lens 222, and prism 228 are collectively andindividually referred to as front-end optics 56.

Referring now to FIG. 9A, a front face view of λ(n) channel MEMS mirror(row A) and five incident beams from the five fiber input fiber ports isillustrated, according to an illustrative embodiment of the presentinvention. Mirrors 72 and 73 (shown in FIG. 9B) of the mirror array arepreferably formed within a single substrate 264 (shown in FIG. 4) in arectangular two-dimensional array, which is arranged in a switching ormonitoring dimension and a wavelength dimension. A typical mirrorreflective surface 270 (shown in FIG. 4), is illustrated in the planview of FIG. 9A, 9B, 9C includes switching mirror array 72 (row A)preferably having dimensions of about 200 micrometers in the x-axisdirection and about 250 micrometers in the y-axis direction. The opticsare designed to irradiate each mirror of switching mirror array 72,preferably with five elliptically shaped spots 320 representing λ(n)from input fiber ports 12-22. As stated earlier, for example, λ1 mirrorof switching mirror array 72 has λ1(12)-λ1(20) from all five input fiberports 12-20 projected onto λ1 mirror surface via beam steering element68, and by tilting λ1 mirror of switching mirror array 72 of switch 10or 11, switches one selected λ1 (12-20) from fiber input fiber ports12-20 to fiber output port 64 and blocks the remaining unselected λ1(s)from input fiber ports 12-20, and so forth for λ2-λn. In addition, thefive elliptically shaped spots 320 are shown in an overlapping manner(as further shown in FIGS. 9C and 12). λ1(12)-λ1(20) represented byspots 320 preferably have a diameter on an x-axis of about 100micrometers and a diameter on a y-axis of 150 micrometers. The MEMSmirrors of switching mirror array 72 preferably spans about 10millimeters in the x-axis direction (into the page in FIG. 2). It iscontemplated by this invention herein that other dimensions and/orshapes are feasible for switching mirror array 72.

Referring now to FIG. 9B, a front face view of a second channel MEMSmirror (row B) and two incident beams from the two monitoring inputfiber ports is illustrated according to an illustrative embodiment ofthe present invention. A typical mirror reflective surface 270 (shown inFIG. 4), is illustrated in the plan view of FIG. 9B a representativemirror of monitoring mirror array 73 (row B) preferably havingdimensions of 200 micrometers in the x-axis direction and 250micrometers in the y-axis direction. The optics are designed toirradiate each mirror of monitoring mirror array 73, preferably with twoelliptically shaped spots 420. As stated earlier, for example λ1 mirrorof monitoring mirror array 73 has λ1(21) and λ1(23) from two monitoringfiber ports 21 and 23 projected onto λ1 mirror surface via beam steeringelement 68, and by tilting λ1 mirror of monitoring mirror array 73switch 11 switches one selected λ from monitoring fiber ports 21 or 23to output monitoring fiber port 25 and blocks the remaining unselected λfrom monitoring fiber ports 21 and 23 as well as all other λs frommonitoring fiber ports 21 and 23. In addition, the two ellipticallyshaped spots 420 are shown in a non-overlapping manner; however, spots420 may overlap one another on each mirror of monitoring mirror array73. λ1(21) and λ1(23), represented by spots 420 preferably have adiameter on an x-axis about 100 micrometers and a diameter on a y-axisof 150 micrometers. The MEMS mirrors of monitoring mirror array 73 spanabout 10 millimeters in the x-axis direction (into the page in FIG. 2).It is contemplated by this invention herein that other dimensions arefeasible for monitoring mirror array 73.

Referring now to FIG. 9C, a front face view of MEMS mirror 72 (row A)shown with five incident beams from the five input fiber ports isillustrated, according to a preferred embodiment of the presentinvention. As stated earlier, for example, λ1 mirror of switching mirrorarray 72 has λ1(12)-λ1(20) from all five input fiber ports 12-20projected onto λ1 mirror surface via segmented prism beam steeringelement 68, and by tilting λ1 mirror of switching mirror array 72 ofswitch 10 or 11, switches one selected λ1 (12-20) from fiber input fiberports 12-20 to fiber output port 64 and drops the remaining unselectedλ1(s) from input fiber ports 12-20, and so forth for λ2-λn. The fiveincident beams λ1 (12-20) are preferably shown in an overlapping manner.

Referring now to FIG. 10 there is a schematic illustration of a sixinput port by one output fiber port wavelength selective switchdepicting an alternative prior art apparatus for accomplishing an N×1wavelength selective switch. The wavelength selective switch of FIG. 10does not include a beam steering element to focus the beams onto theMEMS mirror array. Rather, the wavelength selective switch of FIG. 10uses a simple lens (or lenses) in its back end optics. Such anembodiment limits the wavelength selective switch of FIG. 10 to a singleN×1 or 1×N architecture, and precludes use of multiple N×1 or 1×Nswitches in a single package, as shown in the other figures.Additionally, wavelength selective switch of FIG. 10 employs a fibercollimating lens array (FCLA) 502 in place of an FCA and FE optics. TheFCLA 502 places a small collimating lens 504 at the output of eachfiber. This combination of FCLA 502 and collimating lens 504 generallyincreases the cost and complexity of the system, especially as morefibers are added, since each fiber requires a dedicated collimating lens504 with varying demanding alignment specifications.

Referring now to FIG. 11 there is an illustration of a typicalsingle-row MEMS mirror array λ1-λn, showing primary axis 506 andoptional secondary axis 508 of rotation. Each 1×N or N×1 switch in thepreferred embodiment uses one such row. A single MEMS chip may haveseveral such rows.

Referring now to FIG. 12 there is a three-dimensional schematic of aMEMS mirror of FIGS. 9A and 9C. As illustrated in FIG. 12 light beamsfrom/to the input/output fibers 1-7 preferably are all steered onto theswitching mirror array 72 by the BSE 68 (as shown in FIGS. 1, 2, and 9C)in an overlapping manner. The seven incident beams to or from the seveninput fiber ports are preferably shown in an overlapping manner. Itshould be recognized that rotation of λn mirror about its primary axis506 couples a selected λn by reflecting such selected λn to the outputfiber 64 (shown in FIGS. 1 and 2), and thus such rotation determineswhich λn is selected for monitoring or switching. Further, overlappingspots 320 allow more of switching mirror array 72 surface area to beused, allowing for greater tolerance of reflective surface defects ofswitching mirror array 72.

Referring now to FIG. 13 is a schematic illustration of a six input portby one output fiber port wavelength selective switch representing an N×1switch and is an alternative depiction of the preferred embodiment ofthe present invention shown in FIG. 1. This depiction emphasizes thepresent invention's ability to share all free space optics (FSO) 74,including front end optics (FE) 56, dispersive element 62, back endoptics (BE) 66, beam steering element (BSE) 68, and the elimination ofcollimating lenses 504 of FIG. 10.

Referring now to FIG. 14 there is a three-dimensional schematic of awavelength selective switch according to an embodiment of the presentinvention. The wavelength selective switch of FIG. 14 may represent anN×1 or 1×N embodiment of the present invention with element numbering asset forth in FIGS. 1 and 2.

Referring now to FIG. 15 there is a schematic illustration of a dualwavelength selective switch 12 with BSE-based architecture for creatingmanifold or multi-packaged switches within the same package. Terminologyof manifold, co-packaged, and multi-packaged is used inter changeablyherein as one or more optical switches packaged together and comprisingan optical system. FIG. 15 uses the same ‘cutaway’ view as FIGS. 1 and13 (1×N switch 10) to illustrate an advantage of the present invention'sBSE-based architecture for creating manifold or multi-packaged switcheswithin the same package, while reaping the benefits of re-use andsharing of free space optics (FSO) 74 (including front end optics (FE)56, dispersive element 62, back end optics (BE) 66, beam steeringelement (BSE) 68), baseplate, housing, FCA 52, MEMS control circuitry78, common MEMS array although each mirror is dedicated to one manifoldor multi-packaged switch, and input/output fibers (fiber managementfixture) although each fiber is dedicated to one manifold ormulti-packaged switch. By adding an additional row of mirrors 72.1 tothe existing switching mirror array 72, adding additional waveguides toFCA 52, and adding additional facets to BSE 68, a dual or second N×1switch 10.3 is defined and is shown in the lower-left and upper-rightparts of FIG. 15. The wavelength selective switches 10 and 10.3 of FIG.15 operate independently of one another (that is, their light paths donot interact and such switches are capable of independent switching),while sharing the same housing and common components. It should berecognized that BSE 68 is capable of refracting light beams at arbitraryangles; thus, allowing multiple steering points for λn, on multiplemirror rows, to exist. FIG. 15 illustrates a ‘cutaway’ view of onewavelength λn, and that each MEMS mirror shown represents a row ofmirrors coming out of the page, each mirror corresponding to a differentwavelength λn separated out by dispersive element 62 and positioned byBSE 68.

Although this figure depicts two independent switches 10 and 10.3, theconcept can easily be extended to three, four, or an arbitrary number ofswitches by adding more rows of MEMS mirrors 72, more FCA 52 waveguides,and more BSE 68 facets. If desired, each N×1 or 1×N switch in thepackage can have a different value of ‘N’, down to N=1. Also, anyarbitrary combination of N×1 or 1×N configured switches can be used byaltering the external fibering. All of this is possible because of theBSE 68's ability to refract an arbitrary number of rays at arbitraryangles, although at some point of increasing the number of switches BSE68 may become impractically complex.

Use of common components by multiple internal N×1 or 1×N switchesenables advantages in physical size, thermal output, electrical powerconsumption, ease of manufacture, and materials and labor costs, whencompared to a solution involving multiple switches built and packagedindependently.

FIG. 16 illustrates a variation of the BSE-based architecture of theswitch in FIG. 15, in combination with FCLA-based optics with lenslets504 of FIG. 10. The BSE architecture can be used with this type ofoptical input, as well as the FCA 52 and FE 56 shown in FIGS. 1, 2, and15. An advantage of this approach is that the complexity of BSE 68 issignificantly reduced.

Referring now to FIGS. 17A and 17B there is a schematic illustration ofan advantage of the present invention. FIG. 17A is prior art thatillustrates schematically a 4-input-fiber by 4-output-fiber opticalswitch, made up of four 1×N and four N×1 wavelength selectable switches.This is a common switch architecture used in telecom industry. In FIG.17B, is a schematic illustration of the same 4×4 switch 12, bututilizing an embodiment of the present invention of FIG. 15, wherein twoswitches are co-packaged in the same device. It should be recognizedthat the switch shown in FIG. 17B utilizes the advantages listed abovein the description of FIG. 15, compared to the “one-switch-per-device”architecture of FIG. 17A. Although both figures show a 4×4 switch, theconcept can easily be extended to any value of M×N. Likewise, althoughFIG. 17B illustrates two switches in each device, any number of switchescan be combined using the concept of the present invention. Othertelecom architectures that employ multiple optical switches, such asEast-West dual rings, can also benefit from the embodiments of thisinvention.

FIG. 18A is a schematic illustration of additional aspects andadvantages of the present invention. In this embodiment, BSE 68 isconstructed with prisms that direct beams to two rows of mirrors. Thelower row switching mirror array 72 is used to switch 5×1 signals asshown in FIG. 15. The upper row monitoring mirror array 73 is used toswitch 2×1 monitoring beams as a separate switch. The output of the 2×1monitoring switch is directed to a photodetector 79 serving as anintegrated optical power monitor (OPM). By sequentially switching eachmirror 73 in the array to send selected beam to photodetector 79, whiledropping all other wavelengths, such switch obtains, in a short periodof time, the optical power of all wavelengths of monitoring fiber port21. It is contemplated that optical switching and monitoring system iscapable of monitoring two fiber ports 21 and 23 sequentially, and thisconcept is expandable to an arbitrary number of monitoring ports and/orwavelengths. Each wavelength of monitoring fiber port 21 is monitoredone at a time, by tilting monitoring mirror array 73 to the correctangle to couple its light into output monitoring fiber port 25 from tap81, wherein the tapped signal from output fiber port 64 is coupled tomonitoring fiber port 21. It should be recognized that a key advantageof using one WSS as a fiber switch, and the other as a channel selectorfor an OPM, is that the ‘sensor’ and ‘actuator’ of the optical powerfeedback loop are both contained in the same module, and benefit fromre-use of internal components as described above.

Referring now to FIG. 18B there is a physical illustration of apreferred embodiment of FIG. 3A, illustrating the design flexibilityafforded by BSE 68, wherein such BSE 68 is fabricated to have varyingrefraction angles (facet angles). Facet angles of deflection for thefive input fiber wavelengths, two input monitor fiber wavelengths, oneoutput monitoring fiber wavelength, and one output fiber wavelengthmodel preferably are 16.1, 13.3, 6.1, 2.8, 0.00, −2.8, −5.7, −6.5, −7.9degrees. The angles shown in this example correspond to the 5×1 plus 2×1embodiment shown in FIG. 18A. Beam steering element 68 preferablyrefracts wavelength-separated beams from back end optics 66 and steerssuch beams onto switching mirror array 72 and monitoring mirror array 73based on the refractive indices of each segment 68.1-68.9, whetherfocusing all λn beams on a λn mirror of switching mirror array 72,monitoring mirror array 73, or focusing some λn beams onto one mirrorand other λn beams on another mirror or a mirror in a different row.Beam steering element 68 preferably refracts λn from each input port 12,14, 16, 18, 20, 22 onto λn mirror of switching mirror array 72 (as shownin FIG. 9C) of switching mirror array 72 assigned to λn and each λn fromeach input port 21, and 23 onto λn mirror of monitoring mirror array 73.For example, preferably λ1 mirror of switching mirror array 72 hasλ1(12)-λ1(22) from all input fiber ports 12-22 projected onto λ1 mirrorsurface via beam steering element 68, and by tilting λ1 mirror of MEMSswitching mirror array 72, wavelength selective switch 10 preferablyswitches one selected λ1 (12-22) from input fiber ports 12-22 to outputfiber port 64 and blocks the remaining unselected λ1(s) from input fiberports 12-22, and so forth for λ2-λn. Each λn mirror of switching mirrorarray 72, in this example, preferably has five input beams projectedsimultaneously onto the surface of such mirror, all at wavelength λn,wherein those five beams are preferably demultiplexed and focused byfree space optics 74 from input fiber ports 12, 14, 16, 18, 20respectively. In addition, preferably λ1 mirror of monitoring mirrorarray 73 has λ1(21) and λ1(23) from input monitoring fiber ports 21 and23 projected onto λ1 mirror surface via beam steering element 68, and bytilting λ1 mirror of MEMS monitoring mirror array 73, wavelengthselective switch 10 preferably switches one selected λ1 (21-23) frominput monitoring fiber ports 21 and 23 to output monitoring fiber port25 and blocks the remaining unselected λ1(s) from input monitoring fiberports 21 and 23, and so forth for λ2-λn.

Referring now to FIG. 19A, which illustrates the combination switch plusOPM of FIG. 18A, this time with the FCLA 502 and lenslet 504 asillustrated in FIG. 10.

Referring now to FIG. 19B there is illustrated a variation of FIGS. 3Aand 18B, illustrating the design flexibility afforded by BSE 68, byfabricating the BSE with arbitrary refraction angles. The angles shownin this example correspond to the 5×1 plus 2×1 embodiment shown in FIG.19A. It should be recognized from FIGS. 3A, 18B, and 19B that BSE 68 isa versatile element that can be designed with an arbitrary set of prismsto accomplish refraction for a variety of embodiments and variations ofthe present invention. Both “FCA” plus “FE” type optical architecturescan also be accommodated; and arbitrary combinations of N×1 or 1×Nswitches can also be accommodated by changing the number of facetsand/or their refraction angles of BSE 68.

Referring now to FIG. 20 there is an illustration of a variation of theswitch in FIG. 16, in which switching mirror array 72 operates a 1-inputand 6-output optical switch having taps 81 for each of the six outputfiber ports of the top switch. In order to monitor power on all outputfibers for control loop purposes, each output fiber port is tapped usingtaps 81 and fed to a 6-in and 1-out bottom switch co-packaged with thefirst top switch. The 6-in and 1-out switch selects and sends its outputto photodetector 79 for monitoring. Although it is not shown, the sameconcept could be applied to a WSS using “FCA” plus “FE” type opticalarchitecture, and to arbitrary numbers of fibers.

Referring now to FIG. 21 there is a variation of the switch in FIG. 19A,in which power combiner 508 is used to combine all wavelengths from thesix output fiber ports, which are each tapped using taps 81, fed topower combiner 508 and selectively coupled, using power combiner 508, tomonitoring fiber port 21. In this embodiment, the optical switching andmonitoring system has fewer ports than in the example of FIG. 20,possibly reducing the number of components simplifying the design.Although it is not shown, the same concept could be applied to a WSSusing “FCA” plus “FE” type optical architecture, and to arbitrarynumbers of fibers.

Referring now to FIG. 22A there is illustrated an alternative embodimentof the present invention. In FIG. 22A, one of the independent switchesis configured to accept M inputs and focus them onto one row of a firstswitching mirror array 72. Each mirror in switching mirror array 72 (onemirror per wavelength) tilts to select one of the inputs for reflectiononto a fixed (stationary) mirror 510, which can be patterned directlyonto BSE 68 or placed elsewhere in the system. Fixed mirror 510 reflectsthe beam onto one row of a second switching mirror array 72.1. Eachmirror in second switching mirror array 72.1 tilts to the anglenecessary to project its beam to the selected one of N outputs. Thesystem thus operates as an M-input by N-output switch, since any inputcan be coupled to any output. Although it is not shown, the same conceptcould be applied to a WSS using “FCA” plus “FE” type opticalarchitecture, and to arbitrary numbers of fibers. This alternativeembodiment of the present invention is different from the M×N opticalswitches described in U.S. Pat. No. 6,097,859 (Solgaard et al) becauseeach wavelength in the present invention can only exit the unit on oneoutput fiber at a time. In the referenced Solgaard patent, the M×Nestablishes multiple in-to-out paths on the same wavelength; however,the present invention teaches a simpler design, using fewer mirror rows,for example.

Also, in this and other inventions which incorporate two mirrors in thelight path, an additional advantage can be gained when using Pulse WidthModulated (PWM) signals to drive the mirrors, as described in U.S. Pat.Nos. 6,543,286 (Garverick, et al), 6,705,165 (Garverick, et al), and6,961,257 (Garverick, et al). By operating each of the two mirrors inthe path with complementary pulse trains, any insertion loss (IL) ripplecaused by mechanical vibration of the mirrors can be reduced byoperating each mirror with a complementary pulse train. This causes anymechanical vibration in one mirror to occur 180 degrees out of phasewith the other mirror, thus canceling IL ripple in the optical signal.

Referring now to FIG. 22B there is illustrated an alternative embodimentof the present invention which accomplishes the same M×N switchingfunctionality of FIG. 22A. In this embodiment, there is no stationarymirror. Instead the input-side switch is configured as an N×1, and theoutput side as a 1×N. The output of the first switch is coupled to theinput of the second, either by fiber splicing, jumpering via fiberconnectors 83, on-chip patterning of waveguides, or the like. Althoughit is not shown, the same concept could be applied to a WSS using “FCA”plus “FE” type optical architecture, and to arbitrary numbers of fibers.This alternative embodiment of the present invention is different fromthe M×N optical switches described in U.S. Pat. No. 6,097,859 (Solgaardet al) because each wavelength in the present invention can only exitthe unit on one output fiber at a time. In the referenced Solgaardpatent, the M×N establishes multiple in-to-out paths on the samewavelength; however, the present invention teaches a simpler design,using fewer mirror rows, for example.

Referring now to FIG. 23 there is illustrated an alternative embodimentof the present invention. In FIG. 23 the switch is configured as twoidentical, independent switches. In this embodiment first and secondswitching mirror arrays 72 and 72.1 are operated such that they movesynchronously. Although it is not shown, the same concept could beapplied to a WSS using “FCA” plus “FE” type optical architecture, and toarbitrary numbers of fibers, numbers of co-packaged switches, andarbitrary port designations (input versus output)

With respect to the above description then, it is to be realized thatthe optimum dimensional relationships for the parts of the invention, toinclude variations in size, materials, shape, form, position, functionand manner of operation, assembly and use, are intended to beencompassed by the present invention. Moreover, where the references aremade to a 1×5 or 5×1 optical wavelength selective switch, the conceptsare also applicable to other fiber counts such as 1×N, N×1 or N×N.

The invention disclosed and claimed relates to the various modificationsof assemblies herein disclosed and their reasonable equivalents and notto any particular fiber count or wavelength count wavelength selectiveoptical switch. Although the invention has been described with respectto a wavelength selective switch, many of the inventive optics can beapplied to white-light optical switches that do not include wavelengthdispersive elements. Although moveable micromirrors are particularlyadvantageous for the invention, there are other types of MEMS mirrorsthan can be actuated to different positions and/or orientations toaffect the beam switching of the invention.

The foregoing description and drawings comprise illustrative embodimentsof the present invention. Having thus described exemplary embodiments ofthe present invention, it should be noted by those skilled in the artthat the within disclosures are exemplary only, and that various otheralternatives, adaptations, and modifications may be made within thescope of the present invention. Many modifications and other embodimentsof the invention will come to mind to one skilled in the art to whichthis invention pertains having the benefit of the teachings presented inthe foregoing descriptions and the associated drawings. Althoughspecific terms may be employed herein, they are used in a generic anddescriptive sense only and not for purposes of limitation. Accordingly,the present invention is not limited to the specific embodimentsillustrated herein, but is limited only by the following claims.

1. A co-packaged optical switch and optical spectrometer for switchingand monitoring one or more optical signals, the signals comprising oneor more optical wavelengths, each optical wavelength constituting a workpiece, said optical switch and optical spectrometer further comprising:one or more input fiber ports, each said input fiber port serving as anexternal interface for introducing one or more input optical signalsinto said optical switch; one output fiber port, said output fiber portserving as an external interface for extracting the output opticalsignal from said optical switch; one or more shared optical elements,wherein each said optical element focuses the one or more opticalsignals of said one or more input fiber ports and the optical signal ofsaid one output fiber port; at least one shared wavelength dispersiveelement for spatially separating at least one first wavelength of one ofthe one or more input optical signals from at least one other wavelengthof the input optical signal and for recombining at least one firstwavelength of a selected input optical signal of the one or more inputoptical signals with at least one other wavelength of the one or moreinput optical signals to form the output optical signal; an array ofswitching elements, at least one switching element for receiving onewavelength from each of said one or more input fiber ports and forswitching one selected wavelength from one of said one or more inputfiber ports to said one output fiber port according to a position ofsaid at least one switching element; a tap for coupling a portion ofsaid one output fiber port optical signal to at least one inputmonitoring port; at least one moveable reflective element fortranslating laterally across a selected band of the optical spectrum ofsaid portion of said one output fiber port optical signal as projectedby said wavelength dispersive element, and for reflecting a narrow bandof said selected band of the optical spectrum to an output monitoringfiber port according to a position of said moveable reflective element;at least one beam steering element configured to position eachwavelength from each of said one or more input fiber ports onto adesignated switching element of said array of switching elements, toposition at least one selected wavelength from said switching element tosaid output fiber port, and to position the optical spectrum of saidportion of said one output fiber port optical signal projected by saidwavelength dispersive element onto said at least one moveable reflectiveelement; and, an optical measurement device for receiving said narrowband of said selected band of the optical spectrum from said outputmonitoring fiber port and for measuring an optical power of said narrowband of said selected band of the optical spectrum.
 2. The system ofclaim 1, further comprising a position sensing system for measuring aposition of said moveable reflective element.
 3. The system of claim 2,further comprising a controller for correlating the output of saidoptical measurement device with the corresponding output of saidposition sensing system.
 4. The system of claim 3, wherein saidcorrelated outputs of said optical measurement device and saidcorresponding output of said position sensing means are stored in amemory.
 5. The system of claim 3, wherein said correlated outputs ofsaid optical measurement device and said corresponding output of saidposition sensing system are used to display graphically the power levelsof said selected band of the optical spectrum of said output fiber portoptical signal.
 6. The system of claim 3, wherein said correlated outputof said optical measurement device and said corresponding output of saidposition sensing system are used to determine optical parameters of saidoutput fiber port optical signal.
 7. The system of claim 6, wherein saidoptical parameters of said fiber port optical signal are selected from agroup consisting of optical power per wavelength channel, channel centerwavelength, channel passband, channel passband ripple, channel passbandshape, channel crosstalk, and signal to noise ratio, and combinationsthereof.
 8. The system of claim 1, wherein said at least one moveablereflective element is configured for varied speed and direction.
 9. Thesystem of claim 1, wherein said moveable reflective element furthercomprises an electrostatically actuated micro slider.
 10. The system ofclaim 1, wherein said moveable reflective element further comprises arotating cylinder, a slit and a precision stepper motor.
 11. The systemof claim 1, wherein said moveable reflective element is configured tomove to an arbitrary location by a controller and to be held at saidarbitrary location.
 12. The system of claim 1, wherein said opticalmeasurement device is configured to measure spectral regions betweenwavelengths.
 13. The system of claim 1, wherein said optical measurementdevice is configured as an optical spectrum analyzer.
 14. The system ofclaim 9, wherein said electrostatically actuated micro slider comprisesa slider element configured to slide along a substrate, the slidingimplemented with a plurality of electrodes.
 15. The system of claim 9,wherein said electrostatically actuated micro slider further comprises astrip for reflecting said narrow band of said selected band of theoptical spectrum.
 16. The system of claim 10, wherein said rotatingcylinder further comprises a spiral reflector positioned on saidrotating cylinder and is viewable through said slit.
 17. The system ofclaim 14, wherein said precision stepper motor is configured to turnsaid rotating cylinder such that a portion of said spiral reflectorappears to move laterally across said slit.
 18. The system of claim 1,wherein the optical signal paths in said optical switch are reversedsuch that said optical switch comprises one input fiber port and one ormore output fiber ports.
 19. The system of claim 18, further comprising:at least one optical tap on at least one of said one or more outputfiber ports for coupling a portion of said at least one of said one ormore output fiber ports optical signal.
 20. The system of claim 19,further comprising: an optical combiner for receiving one or more saidportion of said at least one of said one or more output fiber portsoptical signal and for combining said one or more said portion of saidat least one of said one or more output fiber ports optical signal. 21.The system of claim 20, wherein said optical combiner couples said oneor more said portion of said at least one of said one or more outputfiber ports optical signal into said input monitoring port for spectralmeasurement by said optical measurement device.